Text book published by Government of Tamil Nadu. This book has been prepared by the Directorate of School Education on behalf of the Government of Tamilnadu. This book has been printed on 60 G.S.M paper. 11th Standard Diamond Chemistry TM / வேதியியல்: dancindonna.info: Mrs. Chitra Malayaman, TamilNadu State Board Syllabus: Books.
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AB curve depicts this. Similarly curve BC represents the increase in vapour pressure of the liquid solvent with increase in temperature. Since the vapour pressure of the solution is always lower than that of its pure solvent, the vapour pressure curve of the solution DE always lie below that of the pure solvent.
D is the point of intersection of the vapour pressure curves of solution and pure solvent. The measured depression in freezing point ATf is found to be directly proportional to the molality m of the solute in solution. It is also the depression in freezing point of one molal solution.
Freezing point depression of a dilute solution is found to be directly proportional to the number of moles and hence the no. Also ATf is independent of the nature of the solute as long as it is non- volatile. Hence depression in freezing point is considered as a colligative property. W1 Kf. Problem 4 1. The freezing point depression constant of benzene is 5. Find the molecular mass of the solute. Beckmann thermometer is not used in determining the absolute value of freezing temperature of the solvent or that of the solution.
It is therefore called a differential thermometer. Temperature differences of even 0. As the capillary has fine bore, a small change of temperature causes a considerable change in the height of mercury column level in the capillary. The whole scale of a Beckmann thermometer covers only about 6K. Initially the level of mercury in the capillary should be on the scale.
This is achieved by transferring mercury from the lower bulb to the reservoir and viceversa. When the Beckmann thermometer is used at high temperatures, some of the mercury from the thermometer bulb is transferred into the upper reservoir. At lower temperature mercury from the reservoir falls down in to the thermometer bulb. Measurement of freezing point depression by Beckmann method A simple Beckmann apparatus is shown in Fig. It consists of a freezing tube a with a side arm c through which a known amount of a solute can be introduced.
A stopper carrying a Beckmann thermometer b and a stirrer d is fitted in to the freezing tube. To prevent rapid cooling of the contents of the freezing tube, A, a guard tube e surrounds the tube so that there is an air space between a and e. It is cooled with gentle and continuous stirring. As a result of super cooling, the temperature of the solvent will fall by about 0. Vigorous stirring is then set in when solid starts separating and the temperature rises to the exact freezing point.
The tube a is taken out, warmed to melt the solid and a known weight of the solute is added through the side arm c. When the solute is dissolved in to the solvent forming a solution, the tube a is put back in to the original position and the freezing point of the solution T is redetermined in the same manner as before.
The difference between the two readings gives the freezing point depression ATf. From this value, the molecular mass of the non-volatile solute can be determined using the expression and known Kf value.
Since the vapour pressure of a solution is always lower than that of the pure solvent, it follows that the boiling point of a solution will always be higher than of the pure solvent.
The lower curve represents the vapour pressure - temperature dependance of a dilute solution with known concentration. It is evident that the vapour pressure of the solution is lower than that of the pure solvent at every temperature. Elevation of boiling point is found directly proportional to the molality of the solution or inturn the number of molecules of solute.
Also it is independent of the nature of the solute for a non-volatile solute. Hence, boiling point elevation is a colligative property. ATb am It is defined as the elevation of boiling point of one molal solution.
Wi 49 Table PtK Kb K. The molal elevation constant of benzene is 2. An inverted funnel tube b placed in the boiling tube collects the bubbles rising from a few fragments of a porous pot placed inside the liquid. When the liquid starts boiling, it pumps a stream of a liquid and vapour over the bulb of the Beckmann thermometer f held a little above the liquid surface.
In this way, the bulb is covered with a thin layer of boiling liquid which is in equilibrium with the vapour. This ensures that the temperature reading is exactly that of the boiling liquid and that superheating is minimum. After determining the boiling point of the pure solvent, a weighed amount of the solute is added and procedure is repeated for another reading.
The vapours of the boiling liquid is cooled in a condenser C which has circulation of water through d and e.
The cooled liquid drops into the liquid in a. To Condenser C Problem 7 Fig. This solution boiled 0. Molal elevation constant for benzene is 2. Calculate the molecular weight of the solute. Molecular weight! The flow of the solvent from its side a to solution side b separated by semipermeable membrane c can be stopped if some definite extra pressure is applied on the solution risen to height h.
This pressure that just stops the flow of solvent is called osmotic pressure of the solution. Osmosis is a process of prime importance in living organisms. The salt concentration in blood plasma due to different species is equivalent to 0. If blood cells are placed in pure water, water molecules rapidly move into the cell. The movement of water molecules into the cell dilutes the salt content.
As a result of this transfer of water molecules the blood cells swell and burst. Hence, care is always taken to ensure that solutions that flow into the blood stream have the same osmotic pressure as that of the blood. Osmosis is also critically involved in the functioning of kidneys.
They are known as isotonic solutions. He concluded that, a substance in solution behaves exactly like gas and the osmotic pressure of a dilute solution is equal to the pressure which the solute would exert if it is a gas at the same temperature occupying the same volume as the solution.
Thus it is proposed 53 that solutions also obey laws similar to gas laws. Boyle's -VantHoff law The osmotic pressure 71 of the solution at constant temperature is directly proportional to the concentration C of the solution. Charle's - Vant Hoff law At constant concentration the osmotic pressure n of the solution is directly proportional to the temperature T.
Determination of molecular weight by osmotic pressure measurement The osmotic pressure is a colligative property as it depends, on the number of solute molecules and not on their identity. The apparatus Fig. The inner tube a is made of semipermeable membrane c with two side tubes. The outer tube b is made of gun metal which contains the solution. The solvent is taken in the inner tube. As a result of osmosis, there is fall of level in the capillary indicator d attached to the inner tube.
The external pressure is applied by means of a piston e attached to the outer tube so that the level in the capillary indicator remains stationary at d. The osmotic pressure is recorded directly and the method is quick. There is no change in the concentration of the solution during the measurement of osmotic pressure.
The osmotic pressure is balanced by the external pressure and there is minimum strain on the semipermeable membrane. Problem 8 lOg of an organic substance when dissolved in two litres of water gave an osmotic pressure of 0. Calculate the molecular weight of the substance.
However, in some cases experimental values of colligative properties differ widely from those obtained theoretically. Such experimental values are referred to as abnormal colligative properties. The abnormal behaviour of colligative properties has been explained in terms of dissociation and association of solute molecules. Dissociation of solute molecules Such solutes which dissociate in solvent water i.
This effect results in an increase in colligative properties obtained experimentally. We can calculate the degree of dissociation a using the equation.
In such case, the number of effective particles increases and therefore observed colligative property is greater than normal colligative property. Problem 9 A 0. Wi Observed molecular mass 1.
Association of the solute molecules Such solute which associate in a solvent show a decrease in number of particles present in solution. This effect results in a decrease in colligative properties obtained experimentally. In this case, the number of particles is reduced to half its original value due to dimerisation.
In such case, the experimental colligative property is less than normal colligative property. Kb M,W, 3.
Depression in freezing point AT f Freezing point of the solution is lower than solvent. Osmotic pressure n Excess pressure applied on the concentrated solution side to stop the osmosis. Abnormal colligative property i Due to dissociation and association of molecules, there is a change in the experimental colligative property value Van't Hoff factor Observed colligative property i — Theoretical colligative property 60 Questions A.
Properties which depend only on number of particles present in solution are called a Additive b Constitutive c Colligative d None 2. In cold countries, ethylene glycol is added to water in the radiators of cars during winters. It results in: Which of the following 0. The Van't Hoff factor of 0. The degree of ionisation of KC1 is a 0.
Fill in the blanks 6. Relative lowering of vapour pressure is equal to in solution. A liquid having high vapour pressure has boiling point.
The least count of Beckmann's thermometer is. Molal elevation constant is a characteristic constant for a given Semipermeable membrane allows the passage of through it. For a deliquescence to occur, the vapour pressure of water in the air must be than that of the saturated solution.
Depression in freezing point is pronounced if camphor is used as a solvent in place of water for same amount of solute and solvent. Every solution behaves as ideal solution. The osmotic pressures of 0. Solutions that have same osmotic pressure are called solutions. Answer the following in one or two sentences What are colligative properties? Define relative lowering of vapour pressure. What do you understand by molal elevation of boiling point?
What are abnormal solutes? Addition of non-volatile solute always increases the boiling point of the solution. Volatile hydrocarbons are not used in the brakes of automobile as lubricant, but non- volatile hydrocarbon are used as lubricants.
Prove that the depression in freezing point is a colligative property. Explain the terms osmosis and osmotic pressure. What are isotonic solutions? What are the advantages of Berkley-Hartley method? Explain how the degree of dissociation of an electrolyte may be determined from the measurement of a colligative property.
Problems The vapour pressure of pure benzene at a certain temperature is mm of Hg. A non- volatile non-electrolyte solid weighing 2. The vapour pressure of the solution is mm of Hg. What is molecular weight of solid substance? Calculate the freezing point of an aqueous solution of a non-electrolyte having an osmotic pressure 2.
What will be the molality of solution? Find the molecular weight of boric acid. A solution containing 6 gm of a solute dissolved in ml of water gave an osmotic pressure of 4.
Calculate the boiling point of the solution. The molal elevation constant for water is 0. Explain briefly on the following Explain the determination of relative lowering of vapour pressure by Ostwald- Walker method? Describe about Beckmann thermometer. Explain the determination of depression in freezing point by Beckmann method. What is elevation of boiling point? Explain its determination by Cottrell's method. Explain the laws of osmotic pressure?
Explain its determination by Berkley-Hartley method.
What are abnormal colligative properties? Explain with example and write its determination using Van't Hoff factor. Physical Chemistry by Lewis and Glasstone. Physical Chemsitry by Maron and Prutton. Physical Chemistry by P. To differentiate system and surroundings from universe. To define various processes, properties; state and path functions; spontaneous and non-spontaneous; exo- and endo-thermic processes.
To learn to interrelate work, heat and energy. To define Zeroth and first laws of thermodynamics. To measure changes in internal energy and enthalpy. To relate E and H. To determine enthalpy changes of various physical processes. To determine enthalpy changes in formation, combustion, neutralisation. To understand non-conventional energy resources and to identify different renewable energy resources. Thermodynamics deals with the inter-relationship between heat and work. It is concerned with the interconversions of one kind of energy into another without actually creating or destroying the energy.
Energy is understood to be the capacity to do work. It can exist in many forms like electrical, chemical, thermal, mechanical, gravitational etc. Transformations from one to another energy form and prediction of the feasibility possibility of the processes are the important aspects of thermodynamics.
As an illustration, from our common experience steam engines are seen to transform heat energy to mechanical energy, by burning of coal which is a fossil fuel. Actually, the engines use the energy stored in the fuel to perform mechanical work.
In chemistry, many reactions are encountered that can be utilised to provide heat and work along with the required products. At present thermodynamics is widely used in physical, chemical 64 and biological sciences focussing mainly on the aspect of predicting the possibility of the processes connected with each sciences. On the other hand, it fails to provide insight into two aspects: Firstly, the factor of time involved during the initial to final energy transformations and secondly, on the quantitative microscopic properties of matter like atoms and molecules.
System Thermodynamically a system is defined as any portion of matter under consideration which is separated from the rest of the universe by real or imaginary boundaries. Surroundings Everything in the universe that is not the part of system and can interact with it is called as surroundings. Boundary Anything fixed or moving which separates the system from its surroundings is called boundary. For example, if the reaction between A and B substances are studied, the mixture A and B, forms the system.
All the rest, that includes beaker, its walls, air, room etc. The boundaries may be considered as part of the system or surroundings depending upon convenience. The surroundings can affect the system by the exchange of matter or energy across the boundaries. Types of systems In thermodynamics different types of systems are considered, which depends on the different kinds of interactions between the system and surroundings.
Isolated system A system which can exchange neither energy nor matter with its surroundings is called an isolated system. For example, a sample in a sealed thermos flask with walls made of insulating materials represents an isolated 65 system Fig.
Closed system A system which permits the exchange of energy but not mass, across the boundary with its surroundings is called a closed system.
For example: A liquid in equilibrium with its vapours in a sealed tube represents a closed system since the sealed container may be heated or cooled to add or remove energy from its contents while no matter liquid or vapour can be added or removed.
Open system A system is said to be open if it can exchange both energy and matter with its surroundings. For eg. Here, matter and heat can be added or removed simultaneously or separately from the system to its surroundings. All living things or systems are open systems because they continuously exchange matter and energy with the surroundings.
A system is said to be heterogeneous, if its contents does not possess the same physical state. For eg: Macroscopic properties of system The properties which are associated with bulk or macroscopic state of the system such as pressure, volume, temperature, concentration, density, viscosity, surface tension, refractive index, colour, etc.
Types of macroscopic properties of system Measurable properties of a system can be divided into two types. Extensive properties The properties that depend on the mass or size of the system are called as extensive properties.
The value of the extensive property is equal to the sum of extensive properties of smaller parts into which the system is divided. Thus volume is an extensive property.
Intensive properties The properties that are independent of the mass or size of the system are known as intensive properties. These properties do not depend on the number of moles of the substance in the system. If any extensive property is expressed per mole or per gram or per ml, it becomes an intensive property. The values of these parameters change when the matter is in liquid state. Thus, the state of a system is defined by specific measurable macroscopic properties of the system.
The initial state of system refers to the starting state of the system before any kind of interaction with its surroundings. The final state of system refers to the state after the interaction of system with its surroundings. A system can interact with its surroundings by means of exchange of matter or heat or energy or all. The variables like P,V,T, composition no.
When the state of the system changes, the values of the state variables of the system also change. Thus, state functions depend only on the initial and final states of system and not on how the changes occur.
Also, if the values of state functions of a system are known, all other properties like mass, viscosity, density etc. For specifying a state of the system, it is not necessary to know all the state variables, since they are interdependent and only a few of them state variables are sufficient. A system which satisfies the conditions of thermal, mechanical and chemical equilibria and contains the macroscopic properties which are independent of time is said to be in thermodynamic equilibrium.
Thermodynamic equilibrium sets the condition that there should be no flow of heat from one portion or part of the system to another portion or part of the same system, ie. Mechanical equilibrium implies that there is no work done by one portion or part of the system over another portion or part of the same system, ie. Pressure of the system being constant at all its points. Chemical equilibrium demands that the composition of one or more phases of chemicals present in the system should remain constant.
Processes starting with the same initial state and ending at different final states correspond to different thermodynamic processes. Different types of processes are commonly used in the study of thermodynamics. Isothermal process is defined as one in which the temperature of the system remains constant during the change from its initial to final states. During the isothermal process, the system exchanges heat with its surroundings and the temperature of system remains constant.
Adiabatic process is defined as that one which does not exchange heat with its surroundings during the change from initial to final states of the system. A thermally and completely insulated system with its surroundings can have changes in temperature during transformation from initial to final states in an adiabatic process.
This is because, the system cannot exchange heat with its surroundings. Isobaric process is that process in which the pressure of the system remains constant during its change from the initial to final state. Isochoric process shows no change in volume of system during its change from initial to final state of the process.
Cyclic process: The process which brings back the system to its original or initial state after a series of changes is called as cyclic process. Spontaneous process are those that occur on their own accord. For example heat flowing from a hotter end of a metal rod to a colder end. In these processes, the transformation of the system from initial, to final state is favourable in a particular direction only.
Many of the spontaneous processes are natural processes and are also, irreversible processes. For example, although carbon burns in air evolving heat to form carbon dioxide, on its own carbon does not catch fire and an initial heat supply is required. Since many of the non- spontaneous processes are slow processes, they also exist as equilibrium processes. Reversible process. In a reversible process the series of changes carried out on the system during its transformation from initial to final state may be possibly reversed in an exact manner.
This is possible when the changes are carried out very slowly in many smaller steps on the system during its change from initial to final state. By doing so, each of its intermediate state will be in equilibrium with its surroundings. Under such conditions the initial and final states of the system become reversible completely. For example, when ice melts a certain amount of heat is absorbed.
The water formed can be converted back to ice if the same amount of heat is removed from it. This indicates that many reversible processes are non- spontaneous processes also. Irreversible Process An irreversible process is one which cannot be retraced to the initial state without making a permanent change in the surroundings. Many of the spontaneous processes are irreversible in nature. Biological ageing is an irreversible process. Water flowing down a hill on its own accord is an irreversible process.
Some of the characteristics of thermodynamically reversible and irreversible processes are compared as below: Reversible process Irreversible process It is a slow process going through a series of smaller stages with each stage maintaining equilibrium between the system and surroundings.
In this process the system attains final state from the initial state with a measurable speed. During the transformation, there is no equilibrium maintained between the system and surroundings. A reversible process can be made to proceed in forward or backward direction.
Irreversible process can take place in one direction only. There is a definite driving force required for the progress of the irreversible process. Work done in a reversible process is greater than the corresponding work done in irreversible process. Work done in a irreversible process is always lower than the same kind of work done in a reversible process.
A reversible process can be brought back to the initial state without making an change in the adjacent surroundings. An irreversible process cannot be brought back to its initial state without making a change in the surroundings.
Exothermic and endothermic processes When the thermodynamic process is a chemical reaction or a physical transformation, process is classified as either exothermic or endothermic depending on the nature of heat involved in the over all process. These two processes are differentiated as follows: Endothermic process Exothermic process A process when transformed from initial to final states by absorption of heat is called as an endothermic process.
A process when transformed from initial to final states by evolution of heat is called as exothermic process. The final state of the system possesses higher energy than the initial state. The excess energy needed is absorbed as heat by the system from the surroundings.
The final state of the system possesses lower energy than the initial state. The excess energy is evolved as heat.
All combustion processes are exothermic. Generally in a physical transformation which is endothermic heat is supplied to bring about the initial to final state. If the physical transformation is exothermic heat is removed to bring about the initial to final state.
Freezing of a liquid at its freezing point is an exothermic process. These variables are classified as state variables or state functions and path variables or path functions. The state functions considered in a gaseous system like, P, V and T are called as state variables. A state function is a thermodynamic property of a system which has a specific value for each state of the system and does not depend on the path or manner in which a particular state is reached.
Other than P,V,T there are other important thermodynamic properties existing as state functions like internal energy U , enthalpy H , free energy G etc. The properties of U,H and G are to be studied later. A path function is a thermodynamic property of the system whose value depends on the path or manner by which the system goes from its initial to final states.
It also depends on the previous history of the system. For example, work w and heat q are some of the thermodynamic properties of the system that are path functions. Their values change when there is a change in manner in which the system goes from initial to final states. For example, if a beaker containing water and a thermometer are the two objects, while reading the temperature of the water in the beaker using the thermometer, a thermal equilibrium is reached between the two objects having a contact with each other.
Also, when the temperatures of the thermometer bulb and that of water in the beaker are same, thermal equilibrium has said to be occurred. It provides a logical basis for the concept of temperature of a system. It can be stated as follows.
Conversely, the Zeroth law can be stated in another manner as, "When two objects are in thermal equilibrium with the third object, then there is thermal equilibrium between the two objects itself. Work w In thermodynamics work is generally defined as the force F multiplied by the distance of displacement s.
Several aspects should be considered in the definition of work which are listed below: Types of work 73 Many types of work are known. Some of the types of work are as follows: If a body of mass v m' is raised through a height v h' against acceleration due to gravity v g', then the gravitational work carried out is v mgh. In this expression, force is v mg' and the distance is v h'. The electrical work is Q. This pressure-volume work is also referred to as the mechanical work.
Heat Like work, heat q is regarded in thermodynamics as energy in transit across the boundary separating a system from its surroundings. Heat changes result in temperature differences between system and surroundings. Heat cannot be converted into work completely without producing permanent change either in the system or in the surroundings.
Some of the characteristics of heat q are: If work is done on the system, the energy of the system increases and v w' is written as a positive quantity. When w or q is positive, it means that energy has been supplied to the system as work or as heat. In such cases internal energy U of the system increases. When w or q is negative, it means that energy is lost by the system as work or as heat. In such cases, the internal energy U of the system decreases. Energy X U' Energy is easily, defined as the capacity to do work.
Whenever there is a change in the state of matter of a system, then there is a change in energy AU of the system. For example energy changes are involved in processes like melting, fusion, sublimation, vapourisation etc.
Energy U exists in many forms. Kinetic energy K. In chemical systems, there are two types of energy available. The energies acquired by the system like electrical, magnetic, gravitational etc. The internal energy is 75 generally referred to as the energy U of a thermodynamic system which is considered to be made up of mainly by P. Characteristics of energy U are: Its value depend on the initial and final states of the system.
Its magnitude depend on the quantity of material in the system. Its value remains constant for fixed initial and final states and does not vary even though the initial and final states are connected by different paths.
There are many ways of enunciating the first law of thermodynamics. Some of the selected statements are given below: Significance of first law of thermodynamics is that, the law ascertains an exact relation between heat and work.
It establishes that ascertain quantity of heat will produce a definite amount of work or vice versa. Also, when a system apparently shows no mechanical energy but still capable of 76 doing work, it is said to possess internal energy or intrinsic energy. To measure heat changes of system at constant pressure, it is useful to define a new thermodynamic state function called Enthalpy V H. H is defined as sum of the internal energy "U' of a system and the product of Pressure and Volume of the system.
H is independent of the path by which it is reached. Enthalpy is also known by the term "heat content'. This is so because, -w indicates that work is done by the system.
Therefore volume increase against constant pressure is considered. Heat effects measured at constant pressure indicate changes in enthalpy of a system and not in changes of internal energy of the system.
Using calorimeters operating at constant pressure, the enthalpy change of a process can be measured directly. Example 1 From the following data at constant volume for combustion of benzene, calculate the heat of this reaction at constant pressure condition. The standard state of a substance at any specified temperature is its pure form at 1 atm pressure.
For example standard state of solid iron at K is pure iron at K and 1 atm. Standard conditions are denoted by adding the superscript to the symbol AH. For a reaction, the standard enthalpy change is denoted by A r H.
Similarly, the standard enthalpy changes for combustion, formation, etc. Generally the reactants are presented in their standard states during the enthalpy change. The following conventions are necessarily adopted in a thermochemical equation: The first reaction can be considered as the formation reaction of water vapour and the second reaction as the formation of liquid water.
Both the reaction refer to constant temperature and pressure. The negative sign of AH indicates that it is an exothermic reaction. The reaction which is exothermic in the forward direction is endothermic in the revere direction and vice-versa.
This rule applies to both physical and chemical processes. These reactions are exothermic in nature.
Enthalpy changes of combustion reactions are used in industrial heating and in rocket fuels and in domestic fuels. Enthalpy change of combustion A C H, of a substance at a given temperature is defined as the enthalpy change of the reaction accompanying the complete combustion of one mole of the substance in presence of excess oxygen at that temperature. These values are useful to experimentally determine the standard enthalpy change of formation of organic compounds.
The inner vessel or the bomb and its cover are made of strong steel. The cover is fitted tightly to the vessel by means of metal lid and screws.
A weighed amount of the substance is taken in a platinum cup or boat connected with electrical wires for striking an arc instantly to kindle combustion. The bomb is then tightly closed and pressurised with excess oxygen.
The bomb is lowered in water which is placed inside the calorimeter. A stirrer is placed in the space between the wall of the calorimeter and the bomb, so that water can be stirred, uniformly. The reaction is started in the bomb by heating the substance through electrical heating.
During burning, the exothermic heat generated inside the bomb raises the temperature of the surrounding water bath. The enthalpy measurements in this case corresponds to the heat of reaction at constant volume. Although the temperature rise is small only by few degrees , the temperature change can be measured accurately using Beckmann thermometer.
Ignition is brought about electrically. The rise in temperature AT is noted. Water equivalent co c of the calorimeter is known from the standard value of enthalpy of combustion of benzoic acid.
Example 2 Calculate the enthalpy of combustion of ethylene at K at constant pressure if its enthalpy of combustion at constant volume is kJ mol". It is found that the enthalpy of neutralisation of a strong acid and a strong base is a constant value equal to This value is independent of the nature of the strong acid and strong base. Strong acids and strong bases exist in the fully ionised form in aqueous solutions as below: During the neutralisation reaction, water and salt existing as ions are produced in solution.
Therefore, irrespective of the chemical nature, the enthalpy of neutralisation of strong acid by strong base is a constant value. At infinite dilutions, complete ionisation of acids and bases are ensured and also the inter ionic interactions exist in the lowest extents.
The first step is the ionisation of weak acid or weak base since these molecules are only partially ionised. Since ionisation of weak acids and weak bases in water are endothermic and some energy will be used up in dissociating weak acid and weak base molecules. Enthalpy of neutralisation of a weak acid or a weak base is equal to Since enthalpy of ionisation of weak acid or base is endothermic it is a positive value, hence enthalpy of neutralisation of a weak acid or base will be lower than the neutralisation of strong acid and strong base.
Example 3 a The measured heats of neutralization of acetic acid, formic acid, hydrocyanic acid, and hydrogen sulphide are Arrange these acids in a decreasing order of strength. What is the heat of ionization of NH4OH? AH neutraiization for all acids have a -ve sign. AH for ionisation of acetic acid. The acid with the lowest positive value of heat of ionization will be the strongest acid. Thus formic acid is the strongest and hydrocyanic acid the weakest acid. The trend in decreasing strength of acids is: The sum of reactions 2 , 3 and 4 should equal reaction 1.
Choose the correct answer: Which of the following is not a state functions? Which of the following is an extensive property? Which of the following is an exothermic reaction? Which of the following is reversible process? In which process, work is maximum? Fill in the blanks 1. Translational energy of molecules is a part of energy of the system. Specific heat of a liquid system is property. Work done in the reversible expansion is 4.
Combustion is an process. Heat of neutralisation of a strong acid is than that of a weak acid. Write in one or two sentence: Name the equipment using which heat of combustion of compounds are determined? Energy can be created and be destroyed. State whether this is true or false. Define zeroth law of thermodynamics. Give the relation between AU and AH. Define an adiabatic process. Write the differences between an exothermic and an endothermic process. What are intensive and extensive properties?.
Define first law of thermodynamics. Explain thermal and mechanical equilibrium processes. Describe a bomb calorimeter and explain how heat of formation of an organic compound is determined. Compare the enthalpy changes that occur between the neutralisation of a strong acid and a weak acid by sodium hydroxide.
Explain the differences seen. Miscellaneous 1. Calculate the enthalpy of combustion of acetic acid 1 when burnt in excess of O2 in a bomb calorimeter. Calculate the enthalpy of ionization of HA. Calculate AU of the reaction. The definitions like system, surroundings, intensive and extensive properties, thermodynamic properties are given with brief explanations. The laws of thermodynamics are explained with simple examples.
To understand thermodynamics, several problems are given both worked out and practice. Thermodynamics by Samuel Glasstone. Physical Chemistry by Castllan. Atkins' Physical Chemistry seventh edition To express equilibrium constant in terms of concentration and partial pressures and inter relate them. After allowing sufficient period of time for the reaction, upon analyses, when A and B are absent in the reaction mixture, then the reaction is understood to be complete and only the presence of C and D will be detected.
For example, when sodium reacts with water, sodium hydroxide and hydrogen gas are produced, and the reverse reaction to form back the reactants never occurs even when the reaction vessel is a closed one. Reactions when go to completion and never proceed in the reverse direction are called as irreversible reactions.
For Example. For example, when Sb and I2 are reacted, 2 HI is formed. Initially the reaction proceeds to form HI until a certain period of time and with further increase in the reaction time, HI molecules dissociate to produce back H2 and I2 in such a way that, the reaction mixture always contain H2, I2 and HI for any length of time until external factors like temperature, pressure, catalyst etc.
Reactions which never proceed to completion in both forward and backward direction are called as Equilibrium reactions. Physical transformations of matter like change of solid to liquid states or liquid to vapour states also take place under equilibrium conditions with both the states of matter being present together.
The knowledge on whether the equilibrium lies in favour of reactants or products under certain experimental conditions is useful to increase yields in industrial processes, to establish the exact proton transfer equilibria in aqueous protein solutions. Since small changes in equilibrium concentration of hydrogen ion may result in protein denaturing and cell damage etc.
This study is also useful or certain acids, bases and salts in water exist in ionic equilibria which control their use as buffers, colour indicators etc. In a reaction when the product molecules never react to produce back the reactants, then such a reaction is called as irreversible reaction. After the completion, only products exist. Chemical equilibrium may be defined as the state of a reversible reaction when the two opposing reactions occur at the same rate and the concentration of reactants and products do not change with time.
The true equilibrium of a reaction can be attained from both sides. The equilibrium concentrations of reactants and products do not change 90 with time. This is because, since the forward reaction rate equals with backward reaction rate as and when the products are formed, they react back to form the reactants in equal capacity.
The equilibrium concentrations of reactants are different from their initial concentrations. The equilibrium concentrations are represented by square brackets with subscript v eq' or as [ ] eq. Thus [A] eq denotes the equilibrium concentration of A in moles per litre.
In modern practice, the subscript v eq' is not used. Apparently, the equilibrium appears as dead or as not proceeding. Actually, the reactant molecules are always reacting to form the product molecules.
When the product molecules are able to react with themselves under the same experimental condition to form the same amount of reactants simultaneously at the same time in an equal rate of the forward reaction, then the process is a ceaseless phenomenon.
Thus chemical equilibrium is dynamic when the forward and reverse reactions take place endlessly and simultaneously with equal rates. Therefore chemical equilibrium is called as dynamic equilibrium. The reaction mixture consisting of reactants and products at equilibrium is called as equilibrium mixture. The concentrations of reactants and products at equilibrium are called as equilibrium concentrations. The state of equilibrium of a reversible reaction can be arrived at whether we start from reactants or products.
In an open vessel, gaseous reactants or products may escape so that no possibility of attaining equilibrium exists. Equilibrium can be attained when all the reactants and products are in contact with each other. Therefore the equilibrium is not changed but the state of equilibrium is attained earlier.
The equilibrium concepts are also applicable to physical state transformations of matter. At 1 atm and at the melting point of a substance, there is a solid-liquid equilibrium existing. Here, both the liquid and ice exist together. Also, at melting point of ice or freezing point of water, the rate of melting of ice equals with rate of freezing of water. With change in pressure the temperature at which this equilibrium onsets changes. For example, solid sulphur exhibits equilibrium with rhombic to monoclinic forms at its transition temperature.
In a chemical reaction existing in equilibrium, if all the reactants and products are present in the same phase, then a homogeneous equilibria is said to have occurred. Here all the reactants and products exist in gaseous state. This is an example of gas-phase equilibrium. The chemical equilibrium in which all the reactants and products are in the liquid phase are referred to as liquid equilibria. Heterogeneous equilibrium In a chemical equilibrium, if the reactants and products are in different phases then heterogeneous equilibrium is said to have occurred.
In , they postulated a generalisation called the Law of Mass action. It states that: By the term "active mass', it is meant the molar concentration i. Law of Mass Action based on the Molecular Collision theory 94 We assume that a chemical reaction occurs as the result of the collisions between the reacting molecules.
Although some of these collisions are ineffective, the chemical change produced is proportional to the number of collisions actually taking place. Thus at a fixed temperature the rate of a reaction is determined by the number of collisions between the reactant molecules present in unit volume and hence its concentration, which is generally referred as the active mass. The subscript v c' indicates that the value is in terms of concentration of reactants and products. Hence [C], [D] [A] and [B] values are the equilibrium concentrations and are equal to equilibrium concentrations.
The general definition of the equilibrium constant may thus be stated as: The product of the equilibrium concentrations of the products divided by the product of the equilibrium concentrations of the reactants, with each concentration term raised to a power equal to the coefficient of the substance in the balanced equation. The numerical quotient of fh is 3 and NH 3 is 2. Thus, the equilibrium constant expression is: The partial pressure of a gas in the equilibrium mixture is directly proportional to its molar concentration at a given temperature.
The total pressure in the reaction flask is 1 atm and the partial pressures of oxygen, SO2 and SO3 at equilibrium are 0. In the ammonia formation reaction, the gaseous chemical equilibrium exists as: Problem 1 Equivalent amounts of hydrogen and iodine are allowed to reach equilibrium at a given temperature. H 2 h HI Initial concentration mol dm 1 1 Equilibrium concentration It is considered as the fraction of total molecules that actually, dissociate into the simpler molecules x has no units.
For all dissociations involving equilibrium state, x is a fractional value. If x is known, K c or K p can be calculated and vice-versa. Let us consider that one mole of H2 and one mole of I2 are present initially in a vessel of volume V dm.
At equilibrium let us assume that x mole of H2 combines with x mole of I2 to give 2x moles of HI. The concentrations of H2, I2 and HI remaining at equilibrium can be calculated as follows: Initial number of moles Number of moles reacted Number of moles remaining at equilibrium Equilibrium concentration According to the law of mass action, H2 g I X 1-x fl-xl V 12 g I X 1-x "1-x. At equilibrium, let us assume that x mole of H2 combines with x mole of I2 to give 2x moles of HI.
Let the total pressure at equilibrium be P atmosphere. The number of moles of H2, I2 and HI present at equilibrium can be calculated as follows: Mole fraction is the number of moles of that individual component divided by the total number of moles in the mixture. The influence of various factors on the chemical equilibrium can be explained as below: The expressions for the equilibrium constants K c and K p involve neither the pressure nor volume term.
So the equilibrium constants are independent of pressure and volume. Pressure has therefore no effect on the equilibrium. In order to maintain the constancy of K c , the increase in the denominator value will be compensated by the corresponding increase in the numerator value.
In other words, the forward reaction will be favoured and there will be corresponding increase in the concentration of HI. A catalyst affects both the forward and reverse reactions to the same extent.
So it does not change the relative amounts of reactants and products at equilibrium. The values of Ke and K p are not affected. However the equilibrium is attained quickly in the presence of a catalyst. This is an example of gaseous homogeneous equilibrium. At equilibrium let x mole dissociates to give x mole of PCI3 and x mole of Cb. The equilibrium concentrations of the components can be given as follows: Mole fraction is the number of moles of that component divided by the total number of moles in the mixture.
The expression for K c contains the volume term and the expression for K p contains the pressure term. Therefore this equilibrium is affected by the total pressure. According to the above equation, increase in the value of P will tend to increase the value of K p. But K p is a constant at constant temperature. Therefore, in order to maintain the constancy of K p the value of x should decrease. Thus, increase in total pressure favours the reverse reaction and decreases the value of x.