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Thermodynamics · Question 76

AIPMT 2000MCQEasy📈 Topic in 12% papers+4−1
1

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

Answer

(1) -731 J

Solution

Label the equations (i), (ii) and (iii). The required equation = (i) − (ii) + (iii):

(i) 2Zn + O2 2ZnO

−(ii) 2ZnS 2Zn + S2

(iii) S2 + 2O2 2SO2

Adding: 2ZnS + 3O2 2ZnO + 2SO2

∵ G is a state function, values combine in the same way:

= (-616) - (-293) + (-408)

= -731 J

Answer: (1)

AIPMT 2000

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2

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
3

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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