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Thermodynamics · Question 75

AIPMT 2001MCQMedium📈 Topic in 12% papers+4−1
1

Enthalpy of CH4 + 12O2 CH3OH is negative. If enthalpy of combustion of CH4 and CH3OH are x and y respectively. Then which relation is correct?

  1. x > y
  2. x < y
  3. x = y
  4. x ≥ y

Answer

(2) x < y

Solution

(i) CH4 + 2O2 CO2 + 2H2O; H = x

(ii) CH3OH + 32O2 CO2 + 2H2O; H = y

By Hess's law, (i) − (ii) gives CH4 + 12O2 CH3OH

⇒ H = x - y

∵ H < 0 ⇒ x - y < 0

∴ x < y

Answer: (2)

AIPMT 2001

Keep practising — Thermodynamics

2

2Zn + O2 2ZnO; = -616 J 2Zn + S2 2ZnS; = -293 J S2 + 2O2 2SO2; = -408 J for the following reaction 2ZnS + 3O2 2ZnO + 2SO2 is

  1. -731 J
  2. -1317 J
  3. -501 J
  4. +731 J
AIPMT 2000
3

The entropy change in the fusion of one mole of a solid melting at 27 (latent heat of fusion is 2930 J mol-1) is :

  1. 9.77 J/mol-K
  2. 10.77 J/mol-K
  3. 9.07 J/mol-K
  4. 0.977 J/mol-K
AIPMT 2000
4

For the reaction, C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(l) which one is true

  1. = - RT
  2. = + RT
  3. = + 2RT
  4. = - 2RT
AIPMT 2000

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