Question

What is the heat of reaction for C2H4 + 3O2 -> 2CO2 + 2H2O, if heat of formation of C2H4, O2, CO2, and H2O are 10 J, 5 J, 6 J and 2 J respectively?

(a) -4 J

(b) -2 J

(c) 0

(d) 4 J

The question was asked in an interview for job.

This interesting question is from Heat (Enthalpy) of Reaction in section Application of Energy Balances in the Absence of Chemical Reactions and Energy Balances: How to Account for Chemical Reaction of Basic Chemical Engineering

Answer 1

Right answer is (a) -4 J

Explanation: Heat of reaction = 2*2 + 2*6 – 10 – 2*5 = -4 J.