Question

Calculate the differences between Qp and Qv, in the following reactions:

a) H₂(g) +1/2O₂ (g) = H₂O (l) at 25^oC

b) Ethyl acetate + water = ethyl alchol + acetic acid at 25^oC

c) Haber synthesis of ammonia, at 400^oC

d) C₆H₁₂O₆ + 6O₂ (g) = 6CO₂ (g) + 6H₂O, at 25^oC

e) alpha quartz = beta quartz, at 846K

Answer 1

Qp - Qv = ΔnRT, where Δn is increase in no. of gaseous moles in the reaction.

a) H₂(g) +1/2O₂ (g) = H₂O (l) at 25 ^oC

Δn = 0 - 1/2 - 1 = -3/2

Qp - Qv = -3/2 * 8.314 * (25+273) = -3716.4 J

b) Ethyl acetate + water = ethyl alchol + acetic acid at 25 ^oC

CH₃COOC₂H₅ +H₂O ---> CH₃COOH + C₂H₅OH

Δn = 0; All components are in liquid state.

Qp - Qv = 0

c) Haber synthesis of ammonia, at 400^oC

N₂ + 3 H₂ → 2 NH₃

Δn = 2 - 1 - 3 = -2

Qp - Qv = -2 * 8.314 * (400+273) /1000 = -11.2 kJ

d) C₆H₁₂O₆ + 6O₂ (g) = 6CO₂ (g) + 6H₂O, at 25 ^oC

Δn = 6 - 6 = 0

Qp - Qv = 0

e) alpha quartz = beta quartz, at 846K

Δn = 0; Both are solids at given temperature

Qp - Qv = 0