Thermodynamics and Thermochemistry 1 Question 11

11. The reaction, MgO(s)+C(s)Mg(s)+CO(g),

for which ΔrH=+491.1 kJ mol1 and ΔrS=198.0JK1 mol1, is not feasible at 298 K.

Temperature above which reaction will be feasible is

(a) 2040.5 K

(b) 1890.0 K

(c) 2380.5 K

(d) 2480.3 K

Show Answer

Solution:

  1. According to Gibbs-Helmholtz equation,

ΔrG=ΔrHTΔrS

For a reaction to be feasible (spontaneous)

ΔrG<0 ΔrHTΔrS<0

Given, ΔrH=+491.1 kJ mol1,

ΔrS=198JK1 mol1

491.1×103T×198<0

T>491.1×103198=2480.3 K

Above 2480.3 K reaction will become spontaneous.