THERMODYNAMICS

1. CHEMICAL ENERGETICS
It is branch of chemistry which deals with the energy changes in a chemical reaction.
2. SYSTEM AND SURROUNDINGS
A. System
It is the specific part of the universe in which energy changes are taking place.
B. Surroundings
It represents the rest of the universe which surrounds the system. Universe = system + surroundings.
C. Types of system
Systems are of three types:
i. Open system: A system is said to be open, if both mass and energy can be exchanged with the surroundings. For example: Boiling of water in beaker, tea in a cup.
ii. Closed system : A system is said to be closed, if only exchange of energy takes place with the surroundings. For example : Heating of liquid in sealed tube, tea in a steel kettle.
iii. Isolated system : A system is said to be isolated, if there is neither exchange of mass nor of energy. For example : Liquid in a sealed thermos flask, tea in a thermos flask.
D. Homogeneous and heterogeneous systems
i. Homogeneous system: In homogeneous system, all the constituents present are in the same phase and the composition of the system is uniform throughout. For example: A mixture of different gases.
ii. Heterogeneous system: In heterogeneous system constituents are present in two or more phases and its composition is not uniform. For example: Mixture of immiscible liquids.
E. State function of state variables
A physical quantity is said to be a state function, if the change in its value during the process depends only upon initial state and final state of the system and do not depend upon the path by which this change has been brought. For example : Pleasure volume, enthalpy, internal energy etc.
Red Alert    
3. INTENSIVE AND EXTENSIVE PROPERTIES
A. Intensive Properties
The properties which don not depend upon either the size of the system or the quantity of matter present in it, are known as intensive properties. For example: Pressure, temperature, density, specific heat, surface tension, viscosity, refractive index, melting and boiling points etc.
B. Extensive properties
The properties which depend upon the quantity of the matter present in the system are known as extensive properties. For example: Mass, volume, energy, enthalpy, work etc.


4. THERMODYNAMIC PROCESSES
A. Isothermal process
i. A process in which temperature of the system does not change throughout the studies is called isothermal process.
ii. dT = 0 and thus dE = 0
iii. It can be achieved by using thermostatic bath.
B. Adiabatic process
i. A process in which exchange of heat between system and surroundings does not take place.
ii. Means q = 0.
iii. It can be achieved by insulting the boundaries of the system.
C. Cyclic process
i. A process in which system returns to the initial state after a series of changes.
ii. There is no change in energy in a cyclic process dE =0
D. Reversible process
i. It is a process carried out infinitesimally slowly so that all changes ocurring in the direct process can be exactly reversed.
ii. The system and the surroundings remain in a state of equilibrium at any stage in the reversible process.
E. Irreversible process
i. It is a process in which the change is brought about rapidly.
ii. System does not have chance to achieve equilibrium.
iii. The force which drives the reactants towards the products is greater than the opposing force which is to cay the reverse process.
F. Isobaric process
A process in which pressure of the system remains constants. dP=0.
G. Isochoric process
A process in which volume of the system remains constant throughout. dV = 0.
Check Your Grasp
1. Which of the following is a close system?
A. Jet engine
B. Tea placed in steel kettle
C. Pressure cooker
D. Rocket engine during propulsion
2. The intensive property among these quantities is
A. mass B. volume
C. enthalpy D. mass/volume
3. Identify the extensive property among the following:
A. temperature B. pressure
C. viscosity D. enthalpy






4. An adiabatic expansion of an ideal gas always has
A. decrease in temperature
B.
C. w = 0
D.
5. During isothermal expansion of an ideal gas, its
A. internal energy increases
B. enthalpy decreases
C. internal energy remains unaffected
D. enthalpy reduces to zero
5. MODES OF EXCHANGE OF ENERGY BETWEEN THE SYSTEM AND SURROUNDINGS
Energy is mainly exchanged as heat and work between the system and the surroundings.
A. As heat energy
i. Heat absorbed by the system is positive; q=+ve
ii. Heat evolved by the system is negative; q= –ve
iii. Heat is not a state function.
B. As work energy
i. Work is not a state function because the amount of work done depends upon the path followed.
ii. Work done by the system is negative.
iii. Work done on the system is positive.
C. Nature of work
Work is expressed as the product of two factors
i.e., W=Intensity factor  capacity factor
Mechanical work = force (F)  displacement (d)
Electrical work = potential difference (E)  charge flow (Q)
Expansion work = pressure (P)  change in volume (
D. Units of work and heat
  Unit of heat
1 Joule = 0.2390 cal
1 litre -  atm =  J = 1.013   erg = 24.206
Unit of both heat and work is joule (J), 1 Joule =  ergs
1 cal = 4.184 J, 1 calorie> 1 Joule > 1 erg.
E. Work done during various types of processes
i. Work done during expansion, w = – PV
ii. Work done during contraction, w = PV
Red Alert
A. Work done in isothermal and reversible expansion of an
Ideal gas, w = –2.303 nRT. log
= –2.303 nRT log
B. Work done in irreversible process
=  at constant volume
 C. Work done in irreversible process

i. If  then  is + ve, i.e. work is done on the system.
ii If  then,  is –ve, i.e. work is done by the system.

iii.  is the poisson ratio =
monoatomic gas
diatomic gas
1.33 polyatomic gas
D. Important results of adiabatic expansion
PVconstant;T constant
constant. W = .
6. SOME THERMODYNAMIC QUANTITIES
A. Internal energy (E)
i. The energy stored within a substance is called its internal energy. It is denoted by symbol ‘E’.
It is the sum of different types of energies.
electronic energy;
nuclear energy, chemical bond energy
potential energy,  kinetic energy
ii. Iinternal energy of final state
Internal energy of initial state,
Internal energy of products
Internal energy of reactants
 iii Internal energy is an extensive property and state function.
iv. For isothermal processes   is negative if energy is evolved  is positive if energy is absorbed.
v.  is the heat energy exchanged between the system and surrounding at constant temperature and volume
vi. The magnitude of internal energy is determined by the state of system i,e. E =
vii. For a cyclic process  and
B. Enthalpy
i. It is the sum of the internal energy and pressure volume work,
ii. Enthalpy is a state function and extensive property.
iii. For adiabatic process   is negative f energy is evolved i,e. for exothermic reactions
is positive if energy is absorbed i.e. for endothermic reactions
iv Change in enthalpy  is the heat energy exchanged between the system and surrounding at constant temperature and pressure
v. Relationship between heat of reaction at constant P and heat of reaction at constant V is.
Red Alert
vi. The change in enthalpy,
Also  For a reaction involving solids, liquids and gases, the value of  is evaluated by the difference in number of moles of gaseous reactants and products.
TRICK
1. When  then  
2. If  then
3. If  then
vii. For reactions involving solids and liquids only,

viii Enthalpy change  is calculated using calorimeter (an open vessel).
ix. Enthalpies of formations of all the elements in their standard state (at 298 K, 1 atm.) are zero.
x. Kirchoff’s equation
1.
2.
Where  are heat of reactions at temperature  and ,  are heat of reactions at temperature

and  are molar specific heats at constant pressure and constant volume respectively.
xi. The relationship between heat of reaction at constant pressure and that at constant volume is
xii. Bomb calorimeter is used to measure the internal energy.
Red Alert
xiii. Internal energy evolved by a substance

Where,
mass of the substance
heat capacity of the calorimeter
rise in temperature
molecular mass of the substance.
Check Your Gasp
6. If a reaction involves only solids and liquids, which of the following is true
A. B.
C. D.
7. Heat exchanged in a chemical reaction at constant temperature and pressure is called
A. entropy change
B. enthalpy change
C. internal energy change
D. free energy change
8. Enthalpy of a reaction  is expressed as
  A.
B.
C.
D.
9. The enthalpy change of a reaction does not depend
A. The state of reactants and products
B. nature of reactants and products
C. different intermediate reactions
D. initial and final enthalpy change of a reaction
10. Enthalpy change ( of a system depends upon its
A. initial state
B. final state
C. both initial and final state
D. none of these
11. The relation between enthalpy (H), pressure (P), volume (V) and internal energy is given by
A. B.
C. D.
12.  is the heat absorbed at constant
A. temperature (T) B. Pressure (P)
C. volume (V) D. T,P and V’
13. Which of the following is not correct about enthalpy?
A. It is an extensive property
B. It is not a state function
C. Its absolute value cannot be determined
D. Enthalpy of a compound = Enthalpy of formation of that compound
7. EXOTHERMIC AND ENDOTHERMIC REACTIONS
A. Exothermic Reactions
These are chemical reactions which proceed with evolution of heat. In other words, heat is given out by the reacting substances and enthalpy of the product is lowered.
Or

Hence  is negative for exothermic reactions. Likewise  is also negative in these reactions.
B. Endothermic Reactions
These are chemical reactions which proceed with absorption of heat by the reacting substances. The enthalpy of the products, therefore, becomes more than the enthalpy of reactants.
Or

Hence  is + ve for endothermic reactions. Likewise  is positive for these reactions.
Red Alert
8. HEAT CAPACITY OF A SYSTEM
The amount of heat required to raise the temperature of the unit mass of the substance (in the system) by one degree (K or 0C). Heat capacity = dQ/dt
If ‘m’ mass of substance absorbs q amount of heat to raise temperature from  to . then heat capacity (C) of a
Substance is given as  
If mass of the substance involved is 1 g, the heat capacity is called specific heat capacity of the system.
Specific heat capacity  
A. Molar heat capacity (C)
i. The amount of heat required to raise the temperature of one mole of a substance (in the system) by 1K.
Molar heat capacity atomic/molar mass
ii. Molar heat capacity = specific heat capacity  molar mass of the substance.
iii. Unit of molar heat capacity CGS unit of molar heat capacity =cal K-1 mol-1. S.I. unit of molar heat capacity
 = JK-1 mol-1
iv. Molar heat capacity is of two types
1. Molar heat capacity at constant volume

2. Molar heat capacity at constant pressure

3. Relationship between  and
This is known as Meyer’s relationship. R = gas constant
Check You Grasp
14. An exothermic reaction is the one in which the reacting substances
A. have more energy than the products
B. have less energy than the products
C. have the same energy as the products
D. are at a higher temperature than the products
15. For an endothermic reaction where  represent the enthalpy of the reaction in kJ/mol, the minimum value for the energy of activation will be
A. less than   B. zero
C. more than   D. equal to
16. The heat required to raise the temperature of 1g of a body by 1K is called
A. specific heat B. thermal capacity
C. water equivalent D. none of these
17. Heat capacity is
A. B.
C. D. none of these
9. THEMOCHEMICAL EQUATION
It is an equation which represents chemical as well as thermal. Changes taking place in a reaction. For example:  kcal. It signifies that 12 g of carbon on reaction with 32.g of  gives 44 g  along with 393.5 kcal of heat evolution.
A. Factors influencing the enthalpy of reaction
i. Physical state of reactants and products:
Since latent heat is involved in the change in the physical state of reactants and products, therefore enthalpy of reaction change with change in the physical state. For example
 kJ
kJ
ii. Quantities of reactants : The change in enthalpy depends upon the quantities of the reactants taking part in the reaction. For example:
kJ
kJ
When the number of moles of reactants are doubled, the enthalpy change also becomes double.
iii. Allotropic modifications of reactants: The enthalpy of reactions are different for the different allotropic forms of a particular substance. For example:


iv. Conditions of temperature and pressure: A chemical reaction has different enthalpies at different temperature and pressure. They are generally expressed under standard conditions of temperature (298 K) and pressure (1 atm).
v. Conditions of constant pressure and volume: The enthalpy of reaction  is expressed at constant pressure. In case, volume is constant, then it is called change in internal energy . The two are related to each other as
 
10. DIFFERENT TYPES OF ENTHALPIES OF REACTIONS
A. Enthalpy of formation
It is enthalpy change that accompanies the formation of one mole of a compound from its constituting elements at a given temperature and pressure. For example:

Standard enthalpy of reaction
= (Standard enthalpies of formation of products)
– (Standard enthalpies of formation of reactants)
(products)  (reactants)
Red Alert
Compounds with high heat of formation are less stable because energy rich state leads to instability.
EXAMPLE
EXAMPLE:1 The enthalpies of formation of  and NO are 28 and 90 kJ  respectively. The enthalpy of the reaction.
is equal to
A. 8 kJ B. 88 kJ
C.  kJ D. 304 kJ
SOLUTION:  …..(i)

By eq.
B. Enthalpy of combustion
It is the enthalpy change that accompanies the combustion of 1 mole of a substance in excess of air or oxygen.


TRICK
The heat of combustion depends upon number of atoms of carbon and hydrogen. The greater the number of carbon and hydrogen atoms the more will be the heat of combustion.
Note
Calorific values
The amount of heat produced when one gram of the substance is completely burnt.
Red Alert
C. Enthalpy of hydrogenation
It is the enthalpy change when one mole of an unsaturated organic compound is fully hydrogenated.


D. Enthalpy of neutralisation
It is the enthalpy change which takes place when one gram equivalent of an acid and a base present in their their dilute aqueous solution neutralise each other.

 
The heat of neutralisation is due to formation of one mole of water.
kJ,
(from acid) (from base).
i. The enthalpy of neutralisation of a strong acid by a strong base is always constant
ii. Enthalpy of neutralisation of weak acid by weak base, strong acid by weak base or weak acid by strong base is always less than 7.1 kJ. This is because some heat is used in the dissociation of weak acid or weak base. So, heat of neutralisation  enthalpy of dissociation of weak component.
iii. Heat of neutralisation of HF is more than 57.1 kJ (68 kJ). This is due to very high heat of hydration of fluoride ions.
EXAMPLE
EXAMPLE:2 Enthalpy of neutralisation of HCl  with NaOH  is x. The heat evolved when 500 mL of 2N HCl  are mixed with 250 mL of 4N NaOH will be
A. 500x B. 100x
C. x D. 10 x
SOLUTION: 250 mL o 4N NaOH = 500 mLof 2N NaOH. This will completely neutralise 500 mL of 2N HCl. Heat evolved from 1000 mL of 1N HCl =x
Heat evolved from 500 mL of 2N HCl=x
E. Enthalpy of solution
It is enthalpy change when one mole of a substance is dissolved in such a large excess of the solvent at a given temperature that the further addition of the solvent does not produce any more heat energy change.
kJ
Red Alert
i. The enthalpies of solution of the hydrated salts like
or   are positive.
ii. The enthalpies of solution of salts which do not form hydrates like , ,  etc are positive i.e. dissolution is endothermic.
iii. The enthalpies of solution of the anhydrous salts like ,  etc. which form hydrates are negative i.e. dissolution is exothermic.
F. Enthalpy of hydration
It is the enthalpy change when one mole of the anhydrous salt changes to a hydrated salt by combining with specific number of moles of water.

kJ/mol
EXAMPLE
EXAMPLE:3 The enthalpy of dissolution of  and  are  and 8.8 kJ  respectively. The enthalpy of hydration for
(s)+ is
A. 29.4 kJ B.  kJ
C.  kJ D. 38.2 kJ
SOLUTION: Given
kJ. ….(i)
kJ …..(ii)
eq. (i) can be split in two steps as

 

Or

Red Alert
G. Bond Enthalpies
i. Diatomic molecules : The amount of energy required to break one mole bonds of a particular type between two atoms in gaseous state of a substance.
For example:
kJ
ii. Polyatomic molecules: The average of the bond dissociation energy of the bonds of the same type in a gaseous substance. For example:



Bond energy of  bond
kJ
H. Energetic of Phase changes
i. Enthalpy of fusion: It is the change in enthalpy when one mole of a solid at its melting point changes to the liquid state.

ii. Enthalpy of vaporisation : It is the change in the enthalpy when one mole of a liquid at its boiling point changes to the gaseous state.


Check Your Grasp
18. Which one of the following bonds has the highest average bond energy ?
A. S = O B. C = C
C. C  N D. N  N
19. The heat of neutralisation is maximum when
A. sodium hydroxide is neutralised by acetic acid
B. ammonium hydroxide is neutralised by acetic acid
C.  ammonium hydroxide is neutralised by hydrochloric acid.
D. sodium hydroxide is neutralised by hydrochloric acid
20. The neutralisation of a strong acid by a strong base liberates an amount of energy per mole of
A. depends upon which acid and base are involved
B. depends upon the temperature at which the reaction takes place
C. depends upon which catalyst is used
D. is always the same.
21. The enthalpy of neutralisation of a weak acid by a strong base is
A.  kJ B.  kJ
  C. equal to  kJ + enthalpy of ionisation of weak base
D. more than  kJ
11. FIRST LAW OF THERMODYNAMICS
Energy cannot be created or destroyed, although one form of energy can be converted into the other form and vice versa.
A. Mathematical representation of the first law of thermodynamics
Suppose a system has internal energy . If it absorbs heat energy  from the surrounding and (w) work is done on the system, then its final internal energy  becomes
Change in internal energy = Heat energy added to the system + work done on the system.
B. Limitations of first law of thermodynamics
It provides no information concerning the spontaneity or feasibility of the process.
12. HESS’S LAW OF CONSTANT HEAT SUMMATIONS
The heat energy in a physical process of chemical reactions is quite independent of the manner in which the change has been carried.


Applications of Hess’s law
A. To determine heat of transition i.e., conversion of one allotropic form into another.
B. To determine heat of intermediate steps in a reaction.
C. To calculate heat of a known/unknown reactions.
D. To calculate bond energies.
i. For solving bond energy numericals, use,

Bond energy (reactants) –bond energy (products)
or  (products)
ii. Average bond energy

TRICK
iii. The order of average bond energies for different types of bonds is single bond <double bond <triple bond.
iv. In case of allotropes, the enthalpy of formation of the most stable allotrope is taken as zero e.g., the heat of formation of graphite is zero but of diamond is not zero. Similarly, standard enthalpy of rhombic sulphur is zero.
13. SPONTANEOUS AND NON – SPONTANEOUS PROCESSES
A. Spontaneous process
A process which can either take place by itself no by initiation is called a non-spontaneous process. Spontaneous  process is an irreversible process and may only be reversed by some external agency.
B. Non spontaneous process
 A process which can neither take place by itself nor by initiation is called a non-spontaneous process. The force which is responsible for the spontaneity of a process is called the driving force.
Driving forces for spontaneous processes
i. Tendency to acquire minimum energy
ii. Tendency to acquire maximum randomness
14. ENTROPY
Entropy is a measure of randomness or disorder of the system. It is represented by ‘S’.

Entropy of a reaction decreases with increases in pressure. Entropy is state function; Entropy is extensive property.
Unit of entropy: SI unit of entropy :
A. Entropy changes during phase transformations
i) Entropy of fusion : The entropy of fusion is the change in entropy when one mole of a solid substance changes into liquid form at the melting temperature.

  entropy of fusion
entropy of the solid
entropy of the liquid
melting temperature in kelvin
enthalpy of fusion per mole
ii) Entropy of vaporisation : The entropy of vaporisation is the change in entropy when one mole of liquid change into vapours at its boiling temperature.

Enthalpy of vapoisation per mole
boiling temperature in kelvin
iii) Entropy of sublimation : The entropy of sublimation is the entropy change when one mole of the solid changes into vapour at a particular temperature.

Heat of sublimation at the temperature T.
Entropy change of an ideal gas for 1 mol


At constant T (isothermal process)

At constant volume (isochoric process)

At constant pressure (Isobaric process)

Entropy change : The liquid is heated

Entropy and spontaneity
If  reaction is spontaneous.
reaction is non spontaneous
reaction mixture is at equilibrium
EXAMPLE
EXAMPLE : 4 When one mole of an ideal gas is compressed to half of its initial volume and simultaneously heated to twice its initial temperature the change in entropy (is
A. B.
C. D.
SOLUTION

B. Entropy changes in processes not involving any phase transformation
Entropy increases when number of molecules of products are greater than the number of molecules of reactants.
For example:
15. SECOND LAW OF THERMODYNAMICS
A. The total entropy of the universe must tend to increase in a spontaneous process.

B. Second law of thermodynamics
The entropy of universe always increases in the course of every spontaneous (natural) process i.e.  Entropy change of the universe during a reversible isothermal process is zero.
Red Alert
16. GIBB’S FREE ENERGY AND FREE ENERGY CHANGE
A. Gibb’s free energy
It is the amount of energy available for doing useful work under the conditions of constant temperature and pressure. The Gibb’s free energy is related to both enthalpy and entropy as

Enthalpy of the system.
Entropy of the system
Temperature of the system on Kelvin scale

B. Free energy change and predicting spontaneity of a reaction
Free energy change
This equation is called Gibbs-Helmholtz equation.
i.  is state function. ii.  is an extensive property.
C. Criterion of spontaneity
If  is –ve, the process is spontaneous. If  is +ve, the process is non-spontaneous. If  is zero, the process is in equilibrium.
TRICK
D. Effect of temperature on the spontaneity of a process
Sign of
Sign of
Value of temperature Spontaneity
– + Any Spontaneous
+ – Any Non spontaneous
– – Low Spontaneous
– – High Non spontaneous
+ + Low Non spontaneous
+ + High Spontaneous
E. Physical significance of Gibb’s energy change
(Free energy change and useful work)
 Or
The decrease in the free energy in a system of a process is the measure of maximum useful work done by the system. For electrochemical cells, useful work is the electrical work
cell.
Where  number of moles of electrons involved in the cell  of the cell,  faraday
F. Standard free energy change in terms of standard energy of formation
Standard free energy change is the change in free energy which takes place when the reactants in their standard states are converted into the products, also in their standard states.

standard change in enthalpy
standard change in entropy
standard temperature (298K)
(products)(reactants)
G. Relation between standard free energy change and equilibrium constant

lnK
K =
Where,
R = Gas constant
T = Kelvin temperature
K = Equilibrium constant
Standard free energy change
 Red Alert
log K K Comment
log K=0 1 Amount of amount of
reactant = product
log K >0 Equilibrium mixture is mainly product and reaction is spontaneous
log K <0 Equilibrium mixture is mainly reactants and reaction is non spontaneous
Check Your Grasp
22. According to the second law of thermodynamics, a process (reaction) is spontaneous, if during the process
A. B.
C. D.
23. Considering entropy (S) as a thermodynamic parameter, the criterion for the spontaneity of any process is
A.
B.
C.  only
D.  only
24.  was given by
A. Faraday B. Kirchoff
C. Einstein D. Gibbs-Helmholtz
25. For the equilibrium  (l)   (g) at 1 atm and 298 K,
A. standard free energy change is equal to zero
B. fee energy change is less than zero
C. standard free energy change is less than zero
D. standard free energy change is greater than zero

26. A particular reaction has a negative value for the free energy change. Then at ordinary temperature
A. it has a large – ve value for the entropy change
B. it has a large + ve value for enthalpy change
C. it has small + ve value for enthalpy change
D. it has a + ve value for the entropy change and a – ve value for the enthalpy change
27. For a spontaneous chemical process, the free energy change is
A. positive B. negative
C. zero D. any of the above
28. The occurrence of reaction is impossible if
A. is + ve ;  is also + ve
B.  is – ve ;  is also –ve
C.  is –ve ;  is + ve
D.  is + ve ;  is –ve
29. The free energy change for a reversible reaction at equilibrium is
A. zero B. small positive
C. small negative D. large positive
30. The burning silane is a spontaneous process because the value of  is
A. positive B. negative
C. zero D. not significant
17. THIRD LAW OF THERMODYNAMICS
This law was given by Nernst.
“The entropy of an ideal of perfect crystalline solid may be taken as zero at absolute zero temperature.


A. Application of third law of thermodynamics
It helps in the calculation of absolute entropies of various substances at room temperature or any other temperature.
Entropy at T K;  Entropy at 0K
According to third law of thermodynamics
therefore

Where  is the heat capacity of the substances at constant pressure.
B. Entropy change () for a reaction is
products –  reactants
R log  or R log
n  Rln
? EXCEPTIONS
C. Limitations of third law of thermodynamics
i. Glassy solids even at 0 K has entropy greater than zero.
ii. Solid having mixture of isotopes do not have zero entropy at 0 K. For example : entropy of solid chlorine is not zero at 0 K.
iii. Crystals of  etc. do not have perfect order even at 0 K. Thus, their entropy is not equal to zero.
Misconcepts
1. The concept is standard enthalpy of formation of graphite is zero while that of diamond is not zero but it is equal to 1.816 kJ .
2.  In bomb calorimeter,  Hence  should be equal to . But this is not true because
  holds good only at constant pressure.


At constant pressure,

At constant volume,
 +
Note
1. When a rubber band is stretched, entropy decreases because the macro molecules get uncoiled and hence arranged in a more ordered manner. i.e., randomness decreases.
2. When an egg is boiled, the entropy increases because denaturation occurs resulting into a change of proteins from helical form into random coiled form.
Efficiency of machine (: Fraction of heat absorbed by machine which is converted to useful work.

Heat absorbed from source at temperature
Heat rejected to sink at temperature .
EXAMPLE
EXAMPLE:5 What percent  is of  for a heat engine whose efficiency is 10%?
A. 80% B. 90
C. 10% D. 100%
SOLUTION:
Or
Check Your Grasp
31. According to third law of thermodynamics, which one of the following quantities for a perfectly crystalline solid is zero at absolute zero?
A. Entropy B. Free energy
C. Internal energy D. Enthalpy

32. Formation of ice is a process in which entropy
A. decreases B. increases
C. remain constant D. follows a wave pattern