UNIT 7: Thermodynamics - Online Test

Q1. The enthalpies of formation of Al2O3 and Cr2O3 are – 1596 kJ and – 1134 kJ, respectively. ∆H for the reaction 2Al + Cr2O3 → 2Cr + Al2O3 is
Answer : Option D
Explaination / Solution:

2Al + Cr2O3 2Cr + Al2O3

ΔHr0 = [2ΔHf (Cr) + ΔHf (Al2O3)]– [2ΔHf (Al) + ΔHf

(Cr2O3)] ΔHr0 = [0 + (– 1596 kJ)]– [0 + (– 1134)]

ΔHr0 = – 1596 kJ + 1134 kJ

ΔHr0 = – 462 kJ


Q2. Which of the following is not a thermodynamic function ?
Answer : Option D
Explaination / Solution:
No Explaination.


Q3. If one mole of ammonia and one mole of hydrogen chloride are mixed in a closed container to form ammonium chloride gas, then
Answer : Option D
Explaination / Solution:
No Explaination.


Q4. Change in internal energy, when 4 kJ of work is done on the system and 1 kJ of heat is given out by the system is
Answer : Option C
Explaination / Solution:

ΔU = q + w

ΔU = – 1 kJ + 4 kJ

ΔU = + 3kJ


Q5. The work done by the liberated gas when 55.85 g of iron (molar mass 55.85 g mol–1) reacts with hydrochloric acid in an open beaker at 25° C
Answer : Option A
Explaination / Solution:

Fe + 2HCl → FeCl2 + H2

 1 mole of Iron liberates 1 mole of

Hydrogen gas

 55.85 g Iron = 1 mole Iron

  n = 1

 T = 25° C = 298 K

 w = – P Δ V

w =-P (nRT/P)

 w = – nRT

 w = –1 × 8.314 × 298 J

 w = – 2477.57 J

 w = – 2.48 kJ


Q6. The value of ∆H for cooling 2 moles of an ideal monatomic gas from 125° C to 25° C at constant pressure will be given [CP=5/2 R]
Answer : Option B
Explaination / Solution:

Ti = 125° C = 398 K

Tf = 25° C = 298 K

ΔH = nCp (Tf – Ti)

ΔH = 2x(5/2)R(298-398)

ΔH = – 500 R


Q7. Given that C(g) + O2 (g) → CO2 (g) ∆H0 = – a kJ; 2 CO(g) + O2(g) → 2CO2(g) ∆H0 = –b kJ; Calculate the ∆H0 for the reaction C(g) + ½O2(g) → CO(g)
Answer : Option D
Explaination / Solution:



Q8. When 15.68 litres of a gas mixture of methane and propane are fully combusted at 00 C and 1 atmosphere, 32 litres of oxygen at the same temperature and pressure are consumed. The amount of heat of released from this combustion in kJ is (∆HC (CH4) = – 890 kJ mol–1 and ∆HC (C3H8) = – 2220 kJ mol–1)
Answer : Option D
Explaination / Solution:

Given :

ΔHC (CH4)= – 890 kJ mol–1

ΔHC (C3H8)= – 2220 kJ mol–1




Q9. The bond dissociation energy of methane and ethane are 360 kJ mol–1 and 620 kJ mol–1 respec-tively. Then, the bond dissociation energy of C-C bond is
Answer : Option D
Explaination / Solution:

4EC–H= 360 kJ mol–1

EC–H= 90 kJ mol–1

EC–C + 6 EC–H = 620 kJ mol–1

EC–C + 6 × 90 = 620 kJ mol–1

EC–C + 540= 620 kJ mol–1

EC–C= 80 kJ mol–1


Q10. The correct thermodynamic conditions for the spontaneous reaction at all temperature is
Answer : Option A
Explaination / Solution:
No Explaination.