Question

314 J K^-1 mol^-1

(a) – 18.61 kJ

(b) – 18.86 kJ

(c) – 18.65 kJ

(d) – 18.85 kJ

The question was posed to me in homework.

My doubt stems from Enthalpy Change Due to Reaction in section Energy Balance of Bioprocess Engineering

Answer 1

Correct option is (a) – 18.61 kJ

The best I can explain: The reaction is NH4NO3(s) → N2O(g) + 2 H2O(g)

Given 2 mol of NH4NO3 decomposes, hence multiplying equation by 2

2 NH4NO3(s) → 2 N2O(g) + 4 H2O(g)

Δn = nproduct (g) – nreactant (g) = (2 + 4) -(0) = 6

Work done in chemical reaction is given by

∴ W = – Δn RT = – (6) mol × 8.314 J K^-1 mol^-1 × 373 K = – 18607 J

∴ W = – 18.61 kJ

Negative sign indicates that work is done by the system on the surroundings

Work done by the surroundings on the system in the reaction is – 18.61 kJ.