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 Multiple Choice QuestionsMultiple Choice Questions

1.

Which of the following statements is correct for any thermodynamic system?

  • The internal energy changes in all processes.

  • Internal energy and entropy are state functions.

  • The change in entropy can never be zero.

  • The change in entropy can never be zero.


B.

Internal energy and entropy are state functions.

In thermodynamic system, entropy and internal energy are state functions.

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2.

Which one of the following statements is NOT true about the effect of an increase in temperature on the distribution of molecular speeds in a gas?

  • The most probable speed increases

  • The fraction of the molecules with the most probable speed increases

  • The distribution becomes broader

  • The distribution becomes broader


B.

The fraction of the molecules with the most probable speed increases

Most probable velocity increase and a fraction of a molecule possessing most probable velocity decreases.

163 Views

3.

A system goes from A to B via two processes I and II as shown in the figure. If ∆U1 and ∆U2 are the changes in internal energies in the processes I and II respectively, the

  • ∆U1 = ∆U2

  • relation between ∆U1 and ∆U2 can not be determined

  • ∆U2 > ∆U1

  • ∆U2 > ∆U1


A.

∆U1 = ∆U2

Internal energy is state function

328 Views

4.

Two thermally insulated vessels 1 and 2 are filled with air at temperatures (T1, T2), volume (V1, V2) and pressure (P1, P2) respectively. If the valve joining two vessels is opened, the temperature inside the vessel at equilibrium will be

  • T1 + T2

  • T1 + T2/2

  • fraction numerator straight T subscript 1 straight T subscript 2 space left parenthesis straight P subscript 1 straight V subscript 1 plus straight P subscript 2 straight V subscript 2 right parenthesis over denominator straight P subscript 1 straight V subscript 1 straight T subscript 2 space plus space straight P subscript 2 straight V subscript 2 straight T subscript 1 end fraction
  • fraction numerator straight T subscript 1 straight T subscript 2 space left parenthesis straight P subscript 1 straight V subscript 1 plus straight P subscript 2 straight V subscript 2 right parenthesis over denominator straight P subscript 1 straight V subscript 1 straight T subscript 2 space plus space straight P subscript 2 straight V subscript 2 straight T subscript 1 end fraction

C.

fraction numerator straight T subscript 1 straight T subscript 2 space left parenthesis straight P subscript 1 straight V subscript 1 plus straight P subscript 2 straight V subscript 2 right parenthesis over denominator straight P subscript 1 straight V subscript 1 straight T subscript 2 space plus space straight P subscript 2 straight V subscript 2 straight T subscript 1 end fraction

There will be no change in number of moles if the vessels are joined by the valve. Therefore, from gas equation

PV space equals space nRT
fraction numerator straight P subscript 1 straight V subscript 1 over denominator RT subscript 1 end fraction space plus space fraction numerator straight P subscript 2 straight V subscript 2 over denominator RT subscript 2 end fraction space equals space fraction numerator straight P left parenthesis straight V subscript 1 space plus straight V subscript 2 right parenthesis over denominator RT end fraction space
rightwards double arrow space fraction numerator straight P subscript 1 straight V subscript 1 straight T subscript 2 space plus space straight P subscript 2 space straight V subscript 2 straight T subscript 1 over denominator straight T subscript 1 straight T subscript 2 end fraction space equals fraction numerator space straight P left parenthesis straight V subscript 1 space plus straight V subscript 2 right parenthesis over denominator straight T end fraction
space straight T space equals space fraction numerator straight P left parenthesis straight V subscript 1 space plus straight V subscript 2 right parenthesis straight T subscript 1 straight T subscript 2 over denominator left parenthesis straight P subscript 1 straight V subscript 1 straight T subscript 2 space plus space straight P subscript 2 straight V subscript 2 straight T right parenthesis end fraction

Now, according to Boyle's law (pressure = constant) P1 V1 + P2 V2 = P(V1 + V2 )

Hence comma space straight T equals space fraction numerator left parenthesis straight P subscript 1 straight V subscript 1 space plus straight P subscript 2 straight V subscript 2 right parenthesis straight T subscript 1 straight T subscript 1 over denominator straight P subscript 1 straight V subscript 1 straight T subscript 1 space plus space straight P 2 straight V subscript 2 straight T subscript 1 end fraction

1103 Views

5.

The enthalpies of combustion of carbon and carbon monoxide are -393.5 and -283 kJ mol-1 respectively. The enthalpy of formation of carbon monoxide per mole is

  • 110.5 kJ

  • -110.5 kJ

  • -676.5 kJ

  • -676.5 kJ


B.

-110.5 kJ

left parenthesis straight I right parenthesis space straight C space left parenthesis straight s right parenthesis space plus space straight O subscript 2 space left parenthesis straight g right parenthesis space rightwards arrow with space space on top space CO subscript 2 space left parenthesis straight g right parenthesis end subscript space space semicolon space increment straight H space equals space minus space 393.5 space kJ
left parenthesis II right parenthesis space CO space left parenthesis straight g right parenthesis space plus space 1 half space straight O subscript 2 space left parenthesis straight g right parenthesis space rightwards arrow for space space of space CO space left parenthesis straight g right parenthesis space semicolon space increment straight H space equals space minus 283.0 kJ
substracting space left parenthesis straight I right parenthesis space from space left parenthesis II right parenthesis
left parenthesis III right parenthesis space straight C left parenthesis straight s right parenthesis space plus space 1 half space straight O subscript 2 space left parenthesis straight g right parenthesis space rightwards arrow with space space space on top space CO space left parenthesis straight g right parenthesis space increment straight H space equals space minus space 110.0 space kJ
This equation (III) also represents formation of ore mole of CO and thus enthalpy change is the heat formation of CO (g)
223 Views

6.

The temperature-entropy diagram of a reversible engine cycle is given in the figure. Its efficiency is

  • 1/2

  • 1/4

  • 1/3

  • 1/3


C.

1/3



straight eta space equals space fraction numerator increment straight W over denominator straight Q subscript BC end fraction space equals space fraction numerator begin display style fraction numerator straight S subscript 0 straight T subscript 0 over denominator 2 end fraction end style over denominator begin display style fraction numerator 3 straight S subscript 0 straight T subscript 0 over denominator 2 end fraction end style end fraction
space equals space 1 divided by 3
877 Views

7.

Which of the following is incorrect regarding the first law of thermodynamics?

  • It introduces the concept of internal energy

  • It introduces the concept of entropy

  • It is not applicable of any cyclic process

  • It is not applicable of any cyclic process


B.

It introduces the concept of entropy

225 Views

8.

If the bond dissociation energies of XY, X2 and Y2 (all diatomic molecules) are in the ratio of 1:1:0.5 and ∆f H for the formation of XY is -200 kJ mole-1. The bond dissociation energy of X2 will be

  • 100 kJ mol-1

  • 800 kJ mol-1

  • 300 kJ mol-1

  • 300 kJ mol-1


B.

800 kJ mol-1

XY→ X(g) + Y(g) ; ∆H +a kJ/ mole ............(i)
X2 → 2X; ∆H = +a kJ/mole........(ii)
Y2 → 2Y; ∆H =+0.5a kJ/mole.......(iii)
1 half space straight X subscript 2 space plus 1 half space straight Y subscript 2 space rightwards arrow space XY semicolon
increment straight H space equals space open parentheses plus straight a over 2 plus fraction numerator begin display style 0.5 end style over denominator 2 end fraction straight a minus straight a close parentheses kJ divided by mol
plus straight a over 2 space plus fraction numerator 0.5 straight a over denominator 2 end fraction minus straight a space equals space minus 200
straight a space equals space 800

624 Views

9.

Consider the reaction: N2 +3H2 → 2NH3 carried out at constant temperature and pressure. If ∆H and ∆U are the enthalpy and internal energy changes for the reaction, which of the following expressions is true? 

  • ∆H = 0

  • ∆H = ∆U

  • ∆H < ∆U

  • ∆H < ∆U


C.

∆H < ∆U

∆H = ∆U + ∆nRT
∆n = -2
∆H = ∆U - 2RT
∆H < ∆U

545 Views

10.

The standard enthalpy of formation (∆fHo)  at 298 K for methane, CH4(g), is –74.8 kJ mol–1. The additional information required to determine the average energy for C – H bond formation would be

  • the dissociation energy of H2 and enthalpy of sublimation of carbon

  • latent heat of vapourization of methane

  • the first four ionization energies of carbon and electron gain enthalpy of hydrogen

  • the first four ionization energies of carbon and electron gain enthalpy of hydrogen


A.

the dissociation energy of H2 and enthalpy of sublimation of carbon

304 Views