Question

Calorific value of $H_2$ gas is x kJ/gm. What is heat of formation of $H_{2}O$ ?

• A. $xkJ$
• B. $2xkJ$
• C. $x/2kJ$
• D. $18xkJ$

Answer 1

Answer: (C)

$x/2kJ$

Solution:- (C) $\frac{x}{2}kJ/mol$

As we know that the calorific value of a fuel is same as the heat of combustion.

Given that the calorific value of $H_2$ gas is $xkJ/gm$

Molar mass of $H_2$ gas $=2g$

Therefore, calorific value of $H_2$ gas per mole $=\frac{x}{2}kJ/mol$

Hence the the heat of combustion of $H_2$ is $\frac{x}{2}kJ/mol$.

Combustion of $H_2$-

$H_2+\frac{1}{2}O{]}_2⟶H_{[}2O$

From the above reaction, the heat of formation of $H_{2}O$ is same as the heat of combustion of $H_2$ gas.

Hence the heat of formation of $H_{2}O$ is $\frac{x}{2}kJ/mol$.