Question

In the combustion of $0.4$g of $C{H}_4$, $0.25$ Kcal of heat is liberated. The heat of combustion of $C{H}_4$ is:

• A. $-20$ K. Cal
• B. $-10$ K. Cal
• C. $-2.5$ K. Cal
• D. $-5$ K. Cal

Answer 1

Answer: (B)

$-10$ K. Cal

Solution:- (B) $-10kcal$

Molecular weight of methane $=16g$

Heat liberated in the combustion of $0.4g$ of methane $=0.25kcal$

Heat liberated in the combustion of $16g$ of methane $=\frac{0.25}{0.4}\times 16=10kcal$

Hence the heat of combustion of methane is $-10kcal$ whereas the $-ve$ sign indicates that heat is liberated.