(1) For the given heat of reaction,
i) C(s) + O₂(g) = CO₂(g) + 97 kcal
ii) CO₂(g) + C(s) = 2CO(g) – 39 kcal the heat of combustion of CO(g) is:

The correct answer is: 68 kcal

Substracting equation (ii) from equation (i), we get
C(s) + O₂(g) = CO₂(g) + 97 kcal
CO₂(g) + C(s) = 2CO(g) – 39 kcal
or, –CO₂(g) + O₂(g) = CO₂(g) – 2CO(g) + 136 kcal
or, 2CO(g) + O₂ = 2CO₂(g) + 136 kcal
or, CO(g) + 1/2 O₂(g) = CO₂(g) + 68 kcal
Required value = 68 kcal