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Thermodynamics · Question 65

AIPMT 2003MCQHard📈 Topic in 25% papers+4−1
1

The densities of graphite and diamond at 298 K are 2.25 and 3.31 g cm-3, respectively. If the standard free energy difference ( G ) is equal to 1895 J mol-1, the pressure at which graphite will be transformed into diamond at 298 K is

  1. 11.14 108 Pa
  2. 11.14 107 Pa
  3. 11.14 106 Pa
  4. 11.14 105 Pa

Answer

(1) 11.14 108 Pa

Solution

For 1 mol of carbon (12 g):

Vgraphite = 122.25 = 5.333 cm3

Vdiamond = 123.31 = 3.625 cm3

⇒ V = 3.625 - 5.333 = -1.708 cm3 = -1.708 10-6 m3 mol-1

∵ At constant temperature dG = V dP, the extra pressure P must make the work term equal to G :

P | V| = G

⇒ P = 1895 J mol-11.708 10-6 m3 mol-1

⇒ P 1.11 109 Pa = 11.1 108 Pa

∴ The closest value is 11.14 108 Pa.

Answer: (1)

AIPMT 2003

Keep practising — Thermodynamics

2

What is the entropy change (in J K-1 mol-1) when one mole of ice is converted into water at 0 C? (The enthalpy change for the conversion of ice to liquid water is 6.0 kJ mol-1 at 0 C).

  1. 20.13
  2. 2.013
  3. 2.198
  4. 21.98
AIPMT 2003
3

For which one of the following equations is H react equal to H f for the product ?

  1. Xe(g) + 2F2(g) XeF4(g)
  2. 2CO(g) + O2(g) 2CO2(g)
  3. N2(g) + O3(g) N2O3(g)
  4. CH4(g) + 2Cl2(g) CH2Cl2(l) + 2HCl(g)
AIPMT 2003
4

The molar heat capacity of water at constant pressure, C, is 75 J K-1 mol-1. When 1.0 kJ of heat is supplied to 100 g of water which is free to expand, the increase in temperature of water is

  1. 1.2 K
  2. 2.4 K
  3. 4.8 K
  4. 6.6 K
AIPMT 2003
5

Unit of entropy is

  1. J K-1 mol-1
  2. J mol-1
  3. J-1 K-1 mol-1
  4. J K mol-1
AIPMT 2002
6

In a closed insulated container a liquid is stirred with a paddle to increase the temperature. Which of the following is true?

  1. E = W 0, q = 0
  2. E = W = q 0
  3. E = 0, W = q 0
  4. W = 0, E = q 0
AIPMT 2002
7

Heat of combustion Ho for C(s), H2(g) and CH4(g) are -94, -68 and -213 kcal/mol, then Ho for C(s) + 2H2(g) CH4(g) is

  1. -17 kcal
  2. -111 kcal
  3. -170 kcal
  4. -85 kcal
AIPMT 2002
8

2 moles of an ideal gas at 27 temperature is expanded reversibly from 2 lit. to 20 lit. Find entropy change. (R = 2 cal/mol K)

  1. 92.1
  2. 0
  3. 4
  4. 9.2
AIPMT 2002
9

Change in enthalpy for reaction, 2H2O2(l) 2H2O(l) + O2(g) if heat of formation of H2O2(l) and H2O(l) are -188 and -286 kJ/mol respectively, is

  1. -196 kJ/mol
  2. +196 kJ/mol
  3. +948 kJ/mol
  4. -948 kJ/mol
AIPMT 2001
10

When 1 mol of gas is heated at constant volume temperature is raised from 298 to 308 K. Heat supplied to the gas is 500 J. Then which statement is correct ?

  1. q = w = 500 J, E = 0
  2. q = E = 500 J, w = 0
  3. q = -w = 500 J, E = 0
  4. E = 0, q = w = -500 J
AIPMT 2001
11

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
AIPMT 2001

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