Important Questions of Thermodynamics Chemistry | Zigya

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271.

The heat of combustion of carbon to CO2 is -395.5 kJ/mol. The heat released upon the formation of 35.2 g CO2 from carbon and oxygen gas is 

  • -315 kJ

  • +315 kJ

  • -630 kJ

  • -630 kJ

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272.

The formation of the oxide ion O2- (g), from oxygen atom requires first an exothermic and then an endothermic step as shown below,

straight O space left parenthesis straight g right parenthesis space plus space straight e to the power of minus space rightwards arrow space straight O to the power of minus left parenthesis straight g right parenthesis semicolon space increment subscript straight f straight H to the power of straight o space equals space minus 141 space kJ space mol to the power of negative 1 end exponent
straight O to the power of minus space left parenthesis straight g right parenthesis space plus straight e to the power of minus space rightwards arrow space straight O to the power of 2 minus end exponent space left parenthesis straight g right parenthesis semicolon space increment subscript straight f straight H to the power of straight o space equals plus 780 space kJ space mol to the power of negative 1 end exponent
Thus, the process of formation of O2- in the gas phase is unfavourable even though O2- is isoelectronic with neon. It is due to the fact that

  • electron repulsion outweighs the stability gained by achieving a noble gas configuration

  • O- ion has comparatively smaller size that oxygen atom

  • oxygen is more electronegative

  • oxygen is more electronegative

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273.

Consider the following processes Δ H (kJ/mol)

1/2 A →                               +150
3B   → 2 C + D                     -125
E + A  → 2D                        +350

For  B + D   → E + 2C, ΔH will be 

  • 525 kJ/mol

  • -175 kJ/mol

  • -325 kJ /mol

  • -325 kJ /mol

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274.

Standard entropies X2, Y2 and XY2 are 60, 40 and 50 J K-1 mol-1 respectively for the reaction

1 half space straight X subscript 2 space plus 3 over 2 space straight Y subscript 2 space leftwards harpoon over rightwards harpoon space XY subscript 3 space semicolon space increment straight H space equals space minus space 30 space kJ comma space to space be space at
equilibrium, the temperature should be

  • 750 K

  • 1000 K 

  • 1250 K

  • 1250 K

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275.

Three moles of an ideal gas expanded spontaneously into the vacuum. The work done will be

  • infinte

  • 3 J

  • 9 J

  • 9 J

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276.

Match List I (equation) with List II (types of the process) and select the correct option.

List I (Equations)
List II (Types of process)

A

KP > Q

1

Non-spontaneous

B

ΔGo < RT In Q

2

Equilibrium

C

KP = Q

3

Spontaneous and endothermic

D

T> ΔH/ ΔS

4

Spontaneous

  • A
    B
    C
    D
    1
    2
    3
    4
  • A B C D
    3 4 2 1
  • A B C D
    4 1 2 3
  • A B C D
    4 1 2 3
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277.

The values of ΔH and ΔS for the reaction, C(graphite) + CO2(g) → 2 CO (g) are 170 kJ and 170 JK-1 respectively. This reaction will be spontaneous at

  • 710 K 

  • 910 K

  • 1110 K

  • 1110 K

614 Views

278.

Which of the following are not state functions?
I) q + W
II) q
III) W
IV) H-TS

  • (I) and (IV)

  • (II) (III) and (IV)

  • (I), (II) and (III)

  • (I), (II) and (III)

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279.

For the gas phase, reaction,

PCl5 (g) ⇌ PCl3 (g) Cl2 (g)
Which of the following conditions are correct?

  • Δ H = 0 and ΔS > 0

  • ΔH >0 and ΔS > 0

  • Δ H < 0 and ΔS < 0

  • Δ H < 0 and ΔS < 0

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280.

Consider the following reactions:

straight i right parenthesis space straight H to the power of plus space left parenthesis straight g right parenthesis thin space space plus space OH to the power of minus space left parenthesis aq right parenthesis space equals space straight H subscript 2 straight O space left parenthesis straight l right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space increment straight H space equals space minus space straight x subscript 1 space kJ space mol to the power of blank to the power of negative 1 end exponent end exponent
ii right parenthesis space straight H subscript 2 space left parenthesis straight g right parenthesis thin space space plus space straight O subscript 2 space left parenthesis straight q right parenthesis space equals space straight H subscript 2 straight O space left parenthesis straight l right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space increment straight H space equals space minus space straight x subscript 2 space kJ space mol to the power of blank to the power of negative 1 end exponent end exponent
iii right parenthesis space CO subscript 2 space left parenthesis straight g right parenthesis thin space space plus space straight H subscript 2 space left parenthesis straight g right parenthesis space equals space straight H subscript 2 straight O space left parenthesis straight l right parenthesis space plus space CO subscript 2 space left parenthesis straight g right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space increment straight H space equals space minus space straight x subscript 3 space kJ space mol to the power of blank to the power of negative 1 end exponent end exponent
iv right parenthesis straight C subscript 2 straight H subscript 2 space left parenthesis straight g right parenthesis thin space space plus 5 over 2 space straight O subscript 2 space left parenthesis straight g right parenthesis space equals space straight H subscript 2 straight O space left parenthesis straight l right parenthesis space plus 2 CO subscript 2 space left parenthesis straight g right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space increment straight H space equals space plus space straight x subscript 4 space kJ space mol to the power of blank to the power of negative 1 end exponent end exponent
Enthalpy of formation of H2O (l) is:

  • - x2 kJ mol-1

  • + x3 kJ mol-1

  • - x4 kJ mol-1

  • - x4 kJ mol-1


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