Chemical Thermodynamics IIT Part 1

Thermodynamics Part-I: Prepared by V. Aditya vardhan adichemadi(at)gmail.com 1

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NOTE: PART 2 CONTAINS QUESTIONS FROM ENTROPY AND FREE ENERGYThis file was last updated on 5th December, 2009. For the latest updates, visit

http://www.adichemadi.com

CHEMICAL THERMODYNAMICS (PART-I)IIT-JEE

INTRODUCTION & FIRST LAW OF THERMODYNAMICS1) Which of the following statement is true about thermodynamics

a) Thermodynamics will help in predicting whether a physical or chemical change is possible undergiven conditions.b) Thermodynamics only deals with the initial and final states of the system and is not helpful inevolving the mechanism of the process.c) The rate of a reaction can be evolved from thermodynamics.d) The mechanism of a reaction can be evolved from thermodynamics.1) a only 2) a & b 3) a,b & c 4) a & d

2) Choose the incorrect statement1) Open systems can exchange both energy and matter with its surroundings.2) Closed systems can only exchange energy and do not exchange matter with its surroundings.3) Isolated systems can exchange energy and matter with its surroundings.4) None.

3) Which of the following is not an intensive property?1) Entropy 2) Density 3) Temperature 4) Pressure

4) Which of the following is an extensive property?1) Entropy 2) Enthalpy 3) Volume 4) All

5) Extensive properties, out of a) boiling point, b) viscosity, c) pH, d) emf of a cell and e) molar heatcapacity; are1) a, b & c 2) b & e 3) c & e 4) None

6) Which of the following is not a state function?1) Internal energy 2) Enthalpy 3) Work 4) Free energy

7) Which of the following is a state function and not an intensive property?1) Temperature 2) Volume 3) Pressure 4) None

8) In an adiabatic process,1) dT = 0 2) dU = 0 3) 0q 4) AllNote: In an adiabatic process, there is no exchange of heat between system and surroundings. Hence dq = 0 and dU = w.However there is change in temperature and internal energy during this process.

9) In which of the following processes, dT =0?1) Adiabatic process 2) Isobaric process 3) Isothermal process 4) Isochoric process

10) In an isochoric process,1) dT = 0 2) dP = 0 3) dV = 0 4) dH = 0Note: in isochoric (dV=0) and isobaric (dP=0) processes, the pressure-volume work is always zero.

11) In a cyclic process,1) dU = 0 2) dH = 0 3) dT = 0 4) All

12) If the systems A and B are in thermal equilibrium with system C, then system A is also in thermalequilibrium with system B. In thermodynamics, this statement is known as1) 1st law 2) 2nd law 3) 3rd law 4) zeroeth law

13) Thermos flask is an example of1) Closed system 2) Open system 3) Isolated system 4) All

14) The correct statement about isothermal process is1) dT = 0 2) dU = 0 3) q = -w 4) All


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15) The statement which is not true according to 1st law of thermodynamics is1) Energy can neither be created nor destroyed although it can be changed from one form to an-other.2) The total energy of the universe is constant.3) The change in the internal energy of a closed system is equal to the sum of heat lost or absorbed bythe system and work either done by the system or done on the system4) The change in internal energy of a system is zero in all the processes

16) The work done during the free expansion of an ideal gas is equal to1) Pext 2) dV 3) dU 4) zero

17) Which of the following is true about isothermal free expansion of a gas?1) dU = 0 2) dT = 0 3) PextdV = 0 4) All

18) The work done during isothermal irreversible change will be given by

1) -Pext(Vf-Vi) 2) 2.303 log f

i

VnRT

V 3) log f

i

VnRT

V 4) zero

Note: In the irreversible process, the work is done against constant external pressure which differs largely from the internalpressure.

19) The work done during an isothermal reversible change will be given by

1) -Pext(Vf-Vi) 2) 2.303 log f

i

VnRT

V 3) log f

i

VnRT

V 4) zero

Note: In case of reversible process, the internal pressure is almost equal to the external pressure. This internal pressure isgiven by nRT / V.

20) Two litres of an ideal gas at a pressure of 10 atm expands isothermally into vacuum until its totalvolume becomes 100 litres.The amount of heat absorbed in the expansion is1) 2.303 J 2) 100 J 3) 90 J 4) NoneNote: As the process is isothermal, q=-w=PdV; And as the expansion is done against zero pressure(Pext=0), the work done aswell as the heat absorbed will be zero.

21) Which of the following statements is true1) The work done in reversible expansion is less than the work done in irreversible expansion.2) The work done in reversible expansion is equal to the work done in irreversible expansion.3) The work done in reversible expansion is greater than the work done in irreversible expansion.4) All.Note: But in case of compression, |wrev| < |wirrev|

22) Ten litres of an ideal gas at a pressure of 10 atm expands isothermally against a constant pressure of1 atm. until its total volume becomes 100 litres.The work done in the expansion is1) -90 L-atm 2) -10 L-atm 3) -23.03 L-atm 4) -230.3 L-atmHint: This is the case of irreversible expansion.

23) Ten litres of an ideal gas at a pressure of 10 atm expands reversibly under isothermal conditions untilits total volume becomes 100 litres.The work done in the expansion is1) -90 L-atm 2) -10 L-atm 3) -230.3 L-atm 4) -100 L-atmNote: The work done is maximum in case of reversible expansion. (negative sign only indicates the work is done by thesystem)

24) The amount of heat absorbed, when 2.5 L of an ideal gas is compressed isothermally under constantatmospheric pressure until the volume becomes 0.5 L is1) 2 J 2) -202.65 J 3) +202.6 J 4) -2 JNote: 1) During isothermal compression, heat is liberated by the system and hence negative with respect to it.

2) 1 L-atm = 101.325 J25) 2 moles of an ideal gas at STP is expanded isothermally in infinitisimally small steps until the volume

is doubled. The amount of heat absorbed during this process is


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1) 1.37 kJ 2) 8.3 kJ 3) -1.37 kJ 4) None26) 1 liter of an ideal gas, initially at a pressure of 10 atm, is allowed to expand at constant temperature

to 10 liters by reducing the external pressure to 1 atm in a single step. The work done during thisprocess is1) 10 L-atm 2) -100 L-atm 3) -9 L-atm 4) 0 L-atm

27) The area of which of the following graph shows PV work done during reversible expansion of idealgas at constant temperature?

28) 25 L of an ideal gas is compressed isothermally under constant atmospheric pressure until the vol-ume becomes 5 L. The change in internal energy is1) 20 J 2) -2026.5 J 3) +2026 J 4) 0 J

29) There is a balloon of given volume, V1, containing a gas at temperature, T1. When the balloon isplaced in a colder room at temperature, T2, the balloon’s temperature starts to drop. What are thesigns of the system’s q, w, and E for this process?1) +q, +w, +E 2) -q, -w, -E 3) -q, -w, +E 4) -q, +w, -E

30) 11.2 L of a hydrogen gas at 273 K temperature and 1 atm of pressure in a sealed rigid container isheated to double its temperature. The change in internal energy dU will be equal to1) +w 2) +q 3) -w 4) -qNote: As the process is isochoric, the change in internal energy is only due to exchange of heat

dU = qv31) An ideal gas at 10 atm pressure and occupying 0.1 L is expanded to 1.1 L by supplying 101.325 J

of heat against constant atmospheric pressure irreversibly. The change in the temperature of the gasduring this process is1) 10 K 2) 1.1 K 3) 1K 4) No changeHint: dU = q+w = 101.325 J + (-101.325 J) = 0

32) A gas is allowed to expand at constant temperature from a volume of 1.0 L to 10.1 L against anexternal pressure of 0.50 atm. If the gas absorbs 250 J of heat from the surroundings, what are thevalues of q, w, andE respectively?1) 250 J, -461 J & -211 J 2) -250 J, -461 J & -711 J3) 250 J, -461 J & -711 J 4) 250 J, -4.55 J & 245 J


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33) In a process, 800 J of heat is absorbed by a system and 350 J of work is done by the system. Thechange in internal energy for the process is1) 350 J 2) 450 J 3) -450 J 4) -350 J

34) When is dHsys= dEsys?1) When qv= qp.2) In reactions involving only liquids and solids.3) In reactions running under a vacuum (P=0).4) All

35) Which of the following reactions could do work of expansion on the surroundings?1) 2CO(g) + O2(g) 2CO2(g)

2) Fe2O3(s) + 2Al(s) Al2O3(s) + 2Fe(s)3) CH4(g) + 2O2(g) CO2(g) + 2H2O(g)4) 2N2O(g) 2N2(g) + O2(g)

36) Suppose a gas in a piston is expanded at constant pressure and the temperature goes down. Whichof the following correctly describes the signs for the work, the heat for the system and the energychange of the system?1) Work is positive, q is negative, and dU is negative.2) Work is negative, q is may be positive or negative, and dU is negative.3) Work is positive, q is may be positive or negative, and dU is negative.4) Work is positive, q is positive, and dU is negative.

37) In order to have 0E for a process, which of the following conditions must be obeyed ?a) q > 0b) w > 0c) q + w > 0d) q > 0 such that |q| > |w| (where |q| and |w| are absolute values)The correct options are1) a,b,c & d 2) b &d 3) a & d 4) c & d

38) When 2.0 mol O2(g) is heated at a constant pressure of 4.25 atm, its temperature increases from260 K to 285 K. Given that the isobaric molar heat capacity of O2 is 29.4 J.K-1 mol-1, the change inthe internal energy during the process will be1) 1054 J.K-1 mol-1 2) 416 J.K-1 mol-1 3) 1470 J.K-1 mol-1 4) 1887 J.K-1 mol-1

ENTHALPY & HEAT CAPACITY1) The amount of heat exchanged between system and surroundings under constant pressure is called

1) Entropy 2) Enthalpy 3) Internal energy 4) Free energyNote: The amount of heat exchanged at constant pressure i.e.,

pq H U P V

2) Enthalpy(H) of a system can be represented by1) U + PV 2) U-PV 3) q+w 4) dU + PdV

3) Consider the following statements about enthalpy.a) It is an intensive propertyb) It is a state function.c) It is an extensive property.d) It is a path function.The correct statements are1) a & d 2) b & c 3) a & c 4) b & d

4) Hydrogen chloride gas readily dissolves in water, releasing 75.3 kJ/mol of heat in the process. If onemole of HCl at 298 K and 1 atm pressure occupies 24.5 liters, find U for the system when one


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mole of HCl dissolves in water under these conditions.1) +2.48 kJ 2) -75.3 kJ 3) -72.82 kJ 4) +75.3 kJHint: The volume of the liquid is negligible. The process is isothermal and isobaric.Note: -72.82 kJ > -75.3 kJ; So the change in internal energy(dU) will be greater than the change in enthalpy(dH)i.e., dU > dH.But if absolute values are taken, 75.3 kJ > 72.3 kJ i.e., the heat liberated will be greater than decrement in internal energy. Itis because, the compression of the gas which increases the internal energy. Also remember, the magnitude of work done on thesystem is less than heat liberated during the process.

5) One mole of an ideal gas is dissolved in a solvent by liberating 0.27 kJ of heat. What is the change ininternal energy when one mole of gas is dissolved completely in this solvent at 273 K and 1 atmpressure.1) -2 kJ 2) -0.27 kJ 3) +2 kJ 4) +0.53 kJNote: Now +2 kJ > 0.27 kJ. Therefore dU > dH. This is true even when the absolute values are taken. Why? In this case thevalue of work done on the system during compression is greater than the amount of heat lost.

6) If water vapour is assumed to be a perfect gas, molar enthalpy change for vapourisation of 1 mol ofwater at 1bar and 100°C is 41kJ mol-1. The internal energy change, when 1 mol of water is vaporisedat 1 bar pressure and 100°C will be1) 37.9 kJ mol–1 2) 41 kJ mol–1 3) 47.9 kJ mol–1 4) 18.3 kJ mol–1

Reaction: H2(liquid) H2(gas)

Formula:

gWhere n = no. of moles of gaseous products - no. of moles of gaseous reactants

gU H n RT

7) Which of the following is not an intensive property?1) Molar heat capacity 2) Specific heat capacity 3) Heat capacity 4) All

8) The amount of heat required to raise the temperature of 1.00 g of aluminium by 1oC is called its1) Enthalpy 2) Heat capacity 3) Specific heat 4) Molar heat

9) The molar heat capacity for NaCl is 50.50 J mol-1 K-1. What is the specific heat?1) 0.8640 J g-1 K-1 2) 50.5 J g-1 K-1 3) 8.640 J g-1 K-1 4) 4.184 J g-1 K-1

10) The amount of heat necessary to raise the temperature of 60.0 g of aluminium from 15oC to 55oC is.(Molar heat capacity of Al is 24 J mol–1K–1)1) 2.133 J 2) 1.066 J 3) 2.133 kJ 4) 2.4 kJ

Formula: m

m

q=n.C . TWhere n = no. of moles C = molar heat capacity

T = raise or lowering of temperature

11) The heat capacity of methyl alcohol (MW = 32.05 g/mol) is 80.3 J mol-1 K-1. The quantity of heatthat will be evolved when the temperature of 2610 g of methyl alcohol falls from 22oC to 2oC1) 1.5 x 102 kJ 2) 1.3 x 102 kJ 3) 1.7 x 102 kJ 4) 7 kJ

12) The amount of heat absorbed by one mole of an ideal gas in an isochoric process to raise thetemperature from 1.1oC to 11.1oC is 120 kJ/mol. The Cv and Cp values of the gas in kJ mol-1K-1 willbe1) 12 kJ & 3.7 kJ 2) 10 kJ & 12 kJ 3) 12 kJ & 20.3 kJ 4) 20.3 kJ & 12 kJ

Use the formulae:

v

v

v

p

p

p

p v

qUC

T T

qHC

T T

C C nR

13) The difference in Cp and Cv values for liquids and solids will be equal to1) R 2) nR 3) 2R 4) 0

14) Choose the incorrect statement


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1) The molar heat capacities of the metallic elements are almost identical. This is the basis of the Lawof Dulong and Petit, which served as an important tool for estimating the atomic weights of someelements.2) The intermolecular hydrogen bonding in water and alcohols results in anomalously high heatcapacities for these liquids; the same is true for ice, compared to other solids.3) The heat capacity values for graphite and diamond are very high as the solids that are more“ordered” tend to have larger heat capacities.4) None.Note: The molar heat capacities of metals are almost equal to 3R.

15) The molar heat capacity values of noble gases at contant volume are almost equal to

1) 32R

2) 52R

3) 72R

4) R

Note: In case of noble gases (which are mono-atomic) only three translational degrees of freedom are possible and each of

these contribute 1

2R to heat capacity and hence the Cv =

3

2

R . The Cp value will be given by Cv + R =

5

2R

16) The theoretical molar heat capacities of diatomic molecules at constant volume and at fairly hightemperatures is almost equal to

1) 32R

2) R 3) 72R 4)

52R

Note: Diatomic molecules have 3 translational degrees of freedom (contribution of 3R/2), 2 rotational degrees of freedom

(contribution of 1R/2 from each) and 1 vibrational degree of freedom ( contribution of R). Hence Cv = 7

2

R (at high temp.)

But at low temperatures (eg., room temperature), the vibrational degree of freedom can be neglected and hence Cv = 5

2

R

In the same way, for poly-atomic molecules, the contributions are as follows

From three translational degrees of freedom -- 1 1 1 3

2 2 2 2R R R R

From three rotational degrees of freedom -- 1 1 1 3

2 2 2 2R R R R

From 3N-6 vibrational modes -- (3N-6)R (where N = number of atoms in poly-atomic molecule)17) Calculate the enthalpy change on freezing of 1.0 mol of water at10.0oC to ice at –10.0oC. Given

fusH = 6.03 kJ mol–1 at 0°C; Cp [H2O(l)] = 75.3 J mol–1 K–1 ; Cp [H2O(s)] = 36.8 J mol–1 K–1

1) 7.151 kJ 2) -6.03 kJ 3) 3.63 kJ 4) -7.151 kJ18) If 1000 calories are added to 20 g of ice at -10oC, the final temperature will be

(Specific heat of ice = 0.48 cal/g-K and Heat of fusion of ice = 80 cal/g.)1) 380 K 2) 0 K 3) 273 K 4) 283.2 KNote: As the heat supplied is not sufficient to melt the ice completely, finally there will be a mixture of ice and water at 0oC

19) A coffee-cup calorimeter is calibrated by adding 1840 J of heat to the water in the calorimeter andmeasuring a 1.72oC rise in temperature. When some NH4Cl(s) is added to the same water in thecalorimeter, the temperature falls by 1.04oC. The enthalpy change due to the dissolving of NH4Cl(s)is1) -1112 J 2) +1250 J 3) +3040 J 4) +1112 J

20) Which of the following statements is true?1) q = dH at constant P; q = dE at constant T2) q = dH at constant T; q = dE at constant V3) q = dH at constant V; q = dE at constant P4) q = dH at constant P; q = dE at constant V


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21) An ice cube at 0oC weighing 9.0 g is dropped into an insulated vessel containing 72 g of water at50oC. What is the final temperature of water after the ice has melted and a constant temperature hasbeen reached? The latent heat of fusion of ice is 6.01 kJ/mol and the molar heat capacity of H2O is75.4 J mol-1K-1.1) 36oC 2) 40oC 3) 44oC 4) 32oC

22) What is oU when one mole of liquid water vaporises at 100oC if the heat of vaporisation o

vapH

of water at 100oC is 40.66 kJ.mol

-1 ?

1) 40.66 kJ.mol-1 2) 24.66 kJ.mol-1 3) 36.73 kJ.mol-1 4) -40.66 kJ.mol-123) The value of Helium gas is equal to

1) 1.67 cal 2) 1.4 cal 3) 6 cal 4) 10 cal

5Note: 1.67

3

3 For mono atomic gases 3

2 5

p

v

v

p v

Ccal

C

RC cal

C C R cal

24) Temperature of one mole of Neon gas is increased by 1oC, hence, increase in internal energy is1) 5 cal 2) 3 cal 3) 9 cal 4) 2 cal

25) Enthalpy change for a reaction does not depend upon1) the physical states of reactants and products.2) use of different reactants for the same product.3) the nature of intermediate reaction steps.4) the differences in initial or final temperatures of involved substances.

26) The specific heat of water is 4.18 J g-1 K-1 and that of stainless steel is 0.51 J g-1 K-1. The heat thatmust be supplied to a 750.0 g stainless steel vessel containing 800.0 g of water to raise its tempera-ture from 20.0oC to the boiling point of water1) 6.98 kJ 2) 29.8 kJ 3) 69.8 kJ 4) 298 kJ

27) The temperature of a substance represents1) the total heat content of a the particles in a substance2) the speed of the fastest particles in the substance3) the speed of the slowest particles in the substance4) the average kinetic energy of the particles in a system.

28) A bomb calorimeter was calibrated by burning a sample of benzoic acid (C6H5COOH) which hasa known heat of reaction, H° = –3227 kJ/mol. When 1.22 g of benzoic acid is burned in thecalorimeter, the temperature is increased by 0.75 °C. The heat capacity of the calorimeter and itscontents will be1) 32 kJ K-1 2) 4.3 kJ K-1 3) 83 kJ K-1 4) 43 kJ K-1

29) The heat of combustion of methyl alcohol, CH3OH, is -715 kJ mol-1. When 2.85 g of CH3OHwas burned in a bomb calorimeter, the temperature of the calorimeter changed from 24.05 °C to29.19 °C. The heat capacity of the calorimeter is1) 12.4 kJ/°C 2) 124 kJ/°C 3) 12.4 J/°C 4) 1.24 kJ/°C

THERMOCHEMISTRY1) Which statement is incorrect about endothermic reactions?

1) the system absorbs energy from its surroundings2) the enthalpy of products is lower than the enthalpy of the reactants3) the thermal kinetic energy of the surroundings will decrease4) the enthalpy change will have a positive value


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2) Which of the following is the standard state of carbon at STP?1) C as CO2 (g) 2) C as graphite (s) 3) C as CH4 (g) 4) C as diamond (s)

3) Which of the following statements is/are true about an exothermic reaction?I) the energy absorbed in bond breaking is more than the energy released in bond formationII) the system absorbs energyIII) the potential energy of the reactants is less than the potential energy of the productsIV) the thermal kinetic energy of the surroundings will increase1) I and III only 2) II and III only 3) II and IV only 4) IV only

4) How much heat is absorbed when 3.00 grams of SiO2 react with excess carbon according to thereaction below? o

r H for the reaction is +624.7 kJ.SiO2(s) + 3C(s) SiC(s) + 2CO(g)

1) 208 kJ 2) 5.06 kJ 3) 10.4 kJ 4) 31.2 kJ5) H of which of the following reactions is equal to the standard enthalpy of formation( o

f H ) ofNH3?1) 2NH3(g) 3H2(g) + N2(g)2) NH3(g) 3/2H2(g) + 1/2N2(g)3) 3H(g) + N(g) NH3(g)4) 3/2H2(g) + 1/2N2(g) NH3(g)Note: The standard enthalpy of formation, o

fH , is the amount of heat either liberated or absorbed during the formation

of one mole of a compound from its elements under standard conditions.

6) Given: H2(g) + Br2(l) 2 HBr(g) ; or H = –72.8 kJ

Calculate the amount of energy absorbed or released when 15.0 g of HBr (g) is formed.1) 6.75 kJ released 2) 13.5 kJ released 3) 4.85 kJ absorbed 4) 607 kJ absorbed

7) Which of the following has non zero standard enthalpy of formation at 25oC?1) Cl2(g) 2)O2(g) 3) Na(g) 4) F2(g)

8) The standard heat of formation of NH3 is(Given N2(g) + 3H2 (g) 2NH

3 (g) ; o

r H = -91 kJ )1) +91 kJ 2) + 45.5 kJ 3) -19 kJ 4) -45.5 kJ

9) The enthalpy change for the reaction of 50 mL of ethylene with 50 mL of H2 at 1.5 atm pressure isH = -0.31 kJ. The change in internal energy will be

1) 0.66 kJ.mol-1 2) -0.3024 kJ.mol-1 3) +0.3024 kJ.mol-1 4) -0.66 kJ.mol-110) In a constant-volume bomb calorimeter an unknown compound reacted with excess oxygen to give

carbon dioxide and water. The temperature of 2 kg of water in the calorimeter rose from 12.72oCto 20.72oC. The heat capacity of the calorimeter is 2.02 kJ.K-1 and the specific heat of water is4.184 J/goC. The heat given off by the combustion reaction under these conditions is:1) 41,600 J 2) -41.6 kJ 3) -83.2 kJ 4) -33.5 kJNote: The heat given off indicates the internal energy change, as the reaction is occuring at constant volume, andnot is not equal to the enthalpy change.

11) In a constant - volume bomb calorimeter, 4g of methane is burned in excess of oxygen. The tem-perature of 0.5 Kg of water in the calorimeter rose from 12oC to22oC The heat capacity of calorim-eter is 20.1 kJ.K

-1. The enthalpy of combustion of methane under standard conditions will be

1) 223.1 kJ.mol-1 2) 891.6 kJ.mol-1 3) 888 kJ.mol-1 4) 20.92 kJ.mol-1Note: Enthalpy of combustion is the amount of heat liberated when one mole of substance is completely burned in excess ofoxygen at standard conditions (constant temperature and pressure). In this case the amount of heat liberated is equal to U .This value should be converted to H by using the formula.

gH U n RT

12) B5H9 burns in air according to the following reaction.2B5H9(g) + 12O2(g) 5B2O3(s) + 9H2O(l)


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What is the molar heat of reaction for the combustion of B5H9 if the reaction between 0.1 g of B5H9and excess oxygen in a bomb calorimeter raises the temperature of the 852 g of water surroundingthe calorimeter by 1.57oC? [At wts: B = 10.81 amu; H = 1.008 amu; O = 16.00 amu; the heatcapacity of water is 4.184 J / goC]1) 5.60 x 103 J/mol 2) 9.14 x 102 kJ/mol3) 3.54 x 103 kJ/mol 4) 4.46 x 103 kJ/mol

13) In the reaction,CH4(g) + 2O2(g) CO2(g) + 2H2O(l) ; o

r H = -890.4 kJAt 1.0 atm and 273 K , how much work is involved per mole of CH4(g) with the volume change thatoccurs upon reaction.1) -4.5 kJ 2) -2.2 kJ 3) 2.2 kJ 4) 4.54 kJNote: The work is done on the system and is equal to 4.54 kJ. Here gn =-ve and hence, H E i.e., -890.4 kJ< - 885.8 kJ.

But if the absolute values are considered, the decrease in internal energy is less than heat liberated. This is because Someamount of decrease in internal energy, due to loss of heat, is compensated by compression work done on the system.

14) When burned in oxygen, 10.0 g of phosphorus generated enough heat to raise the temperature of2950 g of water from 8.0oC to 28.0oC. The heat of formation of P4O10 from P4(s) and O2(g) is1) -30.6 kJ mol-1 2) -306 kJ mol-1 3) -3060 kJ mol-1 4)-6120 kJ mol-1

15) Using the following data:I) N2(g) + 3O2(g) + H2(g) 2HNO3(aq) ; H = -414.8 kJII) N2O5(g) + H2O(g) 2HNO3(aq) ; H = 218.4 kJIII) 2H2O(g) 2H2(g) + O2(g) ; H = 483.6 kJWhat is the H for the reaction: 2N2O5(g) 2N2(g) + 5O2(g)1) 90.8 kJ 2) -876.4 kJ 3) 782.8 kJ 4)1750 kJ

16.

Which thermochemical equation corresponds to the enthalpy diagram shown above?1) 2 H2 (g) + O2 (g) 2 H2O (g) + 486.3 kJ2) 2 H2 (g) + O2 (g) + 486.3 kJ 2 H2O (g)3) 2 H2 (g) + O2 (g) 2 H2O (g) – 486.3 kJ4) H2 (g) + 1/2 O2 (g) – 486.3 kJ H2O (g)

17. The standard heat of combustion (Hº ) of ethanol is – 1372 kJ/mol ethanol. How much heat isreleased when a 20.0 g sample burns?1) 68.6 kJ 2) 29.8 kJ 3) 3.16 x 103 kJ 4) 595 kJ

18. Which is the correct enthalpy level diagram for the following reaction:CaO(s) + 3C(s) + 462.3 kJ CaC2(s) + CO(g)


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19. Given the following thermochemical equation2 C2H3Br (g) + 5 O2 (g) 4 CO2 (g) + 2 H2O (g) + 2 HBr (g) Hº = 1150 kJWhat is the change in energy accompanying the production of 1.5 moles of CO2(g)?1) 1725 kJ 2) 766.7 kJ 3) 431.3 kJ 4) 9.799 kJ

20. When 1.75 g of CaCl2 dissolves in 125 g of water in a coffee-cup calorimeter, the temperatureincreases by 2.44ºC. What is the heat change per mole of CaCl2 dissolved? Assume that all theheat is absorbed by the water.1) 11.3 kJ/mol of CaCl2 2) 1.13 kJ/mol of CaCl23) 729 kJ/mol of CaCl2 4) 80.9 kJ/mol of CaCl2

21. 5.5 g of sodium hydroxide is dissolved in 175 mL of water. Using a coffee-cup calorimeter, thetemperature change of the water is measured to be +2.10C. The specific heat capacity of wateris 4.184 J/gC. What is the thermochemical equation for this process?1) NaOH(s) NaOH(aq) 1.54 kJ 2) NaOH(s) 1.54 kJ NaOH(aq)

3) NaOH(s) NaOH(aq) 11.2 kJ 4) NaOH(s) 11.2 kJ NaOH(aq)

22. A mass of 100.0 g of dilute hydrochloric acid is placed in a coffee cup calorimeter. The tempera-ture of the solution is recorded to be 17.5C. A piece of magnesium ribbon of mass 0.601 g isplaced in the solution and the final temperature is recorded to be 39.6C. Calculate the molarenthalpy change for this reaction : Mg(s) 2 HCl (aq) MgCl2(aq) H2 (g)

1) + 15.4 kJ/mol of Mg 2) - 263 kJ/mol of Mg3) - 374 kJ/mol of Mg 4) + 5.56 kJ/mol of Mg

23. Which process is not endothermic?1) H2O(s) H2O(l) 2) 2H2O(g) 2H2(g) + O2(g)3) H2O(g) H2O(l) 4) Al2O3 + 2Fe(l) 2Al + Fe2O3

24. Calculate the Ho for the following reaction:2ClF3(g) + 2NH3(g) N2(g) + 6HF(g) + Cl2(g)

Given this information :ClF3(g) f H

o -261.0 kJ/mol

HF(g) f Ho -271.1 kJ/mol

NH3(g) f Ho -46.11 kJ/mol

1) -2241 kJ 2) - 1013 kJ 3) -578.2 kJ 4) 578.2 kJ


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25. Given the thermochemical equation2Al(s) + 3/2O2(g) Al2O3(s) ; Ho = -95.6 kJ

determine Ho for the following reaction2Al2O3(s) 4Al(s) + 3O2(g)

1) -95.6 kJ 2) +95.6 kJ 3) -47.8 kJ 4) +191.2 kJ26. For the reaction:

NH4NO3(s) N2(g) + 2H2O(g) + 1/2O2(g)Ho = -1.50 kJ/g NH4NO3 (molecular mass = 80.05 amu). If 0.105 g NH4NO3 decompose ina bomb calorimeter with a heat capacity of 5.510 J/oC initially at 21.00oC, the final temperature ofthe calorimeter and its contents will be numerically (in K):1) 223 2) 281 3) 323 4) 381

27. Calculate the molar enthalpy of combustion of propylene, C3H6(g), when it reacts with O2(g) togive CO2(g) and H2O(l). [ o

f H (C3H6(g)) = +20.4 kJ/mol, of H (CO2(g)) = -393.5 kJ/mole,

of H (H2O(l)) = -285.8 kJ/mole]

1) +699.7 kJ 2) -658.6 kJ 3) -1926.3 kJ 4) -2018 kJ28. Using the following data:

N2(g) + 3O2(g) + H2(g) 2HNO3(aq) H = -414.8 kJN2O5(g) + H2O(g) 2HNO3(aq) H = 218.4 kJ2H2O(g) 2H2(g) + O2(g) H = 483.6 kJ

Determine H for the reaction:2N2O5(g) 2N2(g) + 5O2(g)

1)149.6 kJ 2) 90.8 kJ 3) -876.4 kJ 4) 782.8 kJ29. Calculate the standard molar enthalpy of formation of CO2(g) in the reaction:

C(s) + O2(g) CO2(g)given the following standard enthalpy changes:

2C(s) + O2(g) 2CO(g) Ho = -221.0 kJ2CO(g) + O2(g) 2CO2(g) Ho = -566.0 kJ

1) -393.5 kJ 2) +393.5 kJ 3) +787.0 kJ 4) -787.0 kJ30. Calculate the Ho for the reaction:

S(s) + O2(g) SO2(g)Given the following data:

S(s) + 3/2O2(g) SO3(g) Ho = -395.2 kJ/mol2SO2(g) + O2 2SO3(g) Ho = -198.2 kJ/mol

1) 592.2 kJ/mol 2) -197.0 kJ/mol 3) -296.1 kJ/mol 4) -593 kJ/mol31. Given the following data:

3/2O2(g) + 2B(s) B2O3(s) Ho = -1264 kJ/molO3(g) + 2B(s) B2O3(s) Ho = -1406 kJ/mol

The change in enthalpy for the reaction converting oxygen (O2(g)) to ozone (O3(g)) at 298 K and1 atm will be

3/2O2(g) O3(g)1) -1406 kJ 2) -1264 kJ 3) -2670 kJ 4) +142 kJ

32. Given the following dataN2(g) + O2(g) 2NO(g) H = 180.8 kJ1/2N2(g) + O2(g) NO2(g) H = 33.9 kJ

calculate the enthalpy change for the following reactionNO(g) + 1/2O2(g) NO2(g)

1) 214.7 kJ 2) 146.9 kJ 3) -56.5 kJ 4) 56.5 kJ


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33. Calculate the enthalpy change, Ho, for the combustion of benzene, C6H6, given the followingC6H6(l) + 15/2O2(g) 6CO2(g) + 3H2O(l)

of H values in kJ/mol are as follows:

C6H6(l) = 49.0; CO2(g) = -393.5; H2O(l) = -285.81) -3169.4 kJ 2) 3267.4 kJ 3) -728.3 kJ 4) -3267.4 kJ

34. Calculate Ho for the reaction: Na2O(s) + SO3 (g) Na2SO4(s) given the following:(1) Na(s) + H2O(l) NaOH(s) + 1/2 H2(g) Ho = – 146 kJ

(2) Na2SO4 (s) + H2O(l) 2NaOH(s) + SO3(g) Ho = + 418 kJ(3) 2Na2O (s) + 2H2(g) 4Na(s) + 2H2O(l) Ho = + 259 kJ

1) + 823 kJ 2) – 581 kJ 3) – 435 kJ 4) + 531 kJ35. Given equations (1) and (2), calculate the enthalpy change for equation (3).

(1) Pb(s) + PbO2(s) + 2 SO3(g) 2 PbSO4(s) Ho = -775 kJ(2) SO3(g) + H2O(l) H2SO4(aq) Ho = -133 kJ(3) Pb(s) PbO2(s) 2 H2SO4(aq) 2 PbSO4(s) 2 H2O(l)

1) – 908 kJ 2) – 642 kJ 3) – 509 kJ 4) + 642 kJ36. Given that : S(s) + O2(g) SO2(g) Hº = – 296.8 kJ/mol

2 SO3(g) 2 SO2(g) + O2(g) Hº = + 197.8 kJ/molDetermine the enthalpy change of the reaction: 2 S(s) + 3 O2(g) 2 SO3(g)1) – 99 kJ 2) – 495 kJ 3) + 495 kJ 4) – 791.4 kJ

37. Use the following reactions to calculate H° for: 4 HCl (g) + O2(g) 2 Cl2(g) + 2 H2O(g)H2(g) + Cl2 (g) 2 HCl(g) H° = – 185.0 kJ2 H2(g) + O2(g) 2 H2O(g) H° = – 483.7 kJ

1) +113.7 kJ 2) –298.7 kJ 3) +298.7 kJ 4) –113.7 kJ38. Given equations (I), (II), and (III), calculate the standard enthalpy of formation of acetylene,

C2H2, as shown in equation (IV).(I) C (s) + O2 (g) CO2 (g) Hº = – 393.5 kJ(II) H2 (g) + ½ O2 (g) H2O (l) Hº = – 285.8 kJ(III) 2 C2H2 (g) + 5 O2 (g) 4 CO2 (g) + 2 H2O (l) Hº = – 2598.8 kJ(IV) 2 C (s) + H2 (g) C2H2 (g)

1) 253.6 kJ 2) 226.6 kJ 3) 1801 kJ 4) -3278 kJ39) A volume of 50.0 mL of 0.5 M NaOH was added to 20.0 mL of 0.5 M H2SO4 in a calorimeter

whose heat capacity is 39.0 J/K. The temperature of the resulting solution increased by 3.6 °C.The standard enthalpy of neutralization of H2SO4(aq) with NaOH(aq) will be1) 13.7 kJ mol-1 2) 53.7 kJ mol-1 3) 5.37 kJ mol-1 4) 23.7 kJ mol-1

40) The standard enthalpy of neutralization of acetic acid with sodium hydroxide will be1) =53.7 kJ mol-1 2) <53.7 kJ mol-1 3) >53.7 kJ mol-1 4) NoneHint: When weak acids or bases participate in the neutralisation, some amount of heat is required for their completedissociation. Hence the amount of heat liberated during neutralisation will be less than 53.7 kJ mol-1.

41) The heat of neutralisation of a strong acid and a strong alkali is 57.0 kJ mol-1. The heat releasedwhen 0.5 mole of HNO3 solution is mixed with 0.2 mole of KOH is1) 57.0 kJ 2) 11.4 kJ 3) 28.5 kJ 4) 34.9 kJ

42) If the bond dissociation energies of XY, X2 and Y2 are in the ratio of 1:2:0.5 and standard heat offormation of XY is -100 kJ mol-1, then the bond dissociation energy of Y2 will be1) 400 kJ mol-1 2) 100 kJ mol-1 3) 200 kJ mol-1 4) 800 kJ mol-1

Chemical Thermodynamics IIT Part 1

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