Question

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:

• A. 68 kcal
• B. – 68 kcal
• C. +48 kcal
• D. None

Answer 1

Answer: (A)

68 kcal

Answer 2

Subtracting 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