Question

The heat of formation of water is $260\, kJ$ . How much $H_2O$ is decomposed by $130\, kJ$ of heat ?

• A. $0.25\, mol$
• B. $1\, mol$
• C. $0.5\, mol$
• D. $2\, mol$

Answer 1

Answer: (C)

$0.5\, mol$

Answer 2

The reaction for the formation of water is as

$H _{2}+\frac{1}{2} O _{2} \to H _{2} O$ ; $\Delta H=260 kJ\, \ldots (i)$

On reversing E (i), we get

$\underset{\text{1 mol}}{H_{2}O} \to H_{2}+\frac{1}{2} O_{2}$;

$\Delta\, H=-260 \,kJ \, \dots(ii)$
$\because$ By $260 \,kJ$ heat water decomposed $=1 \,mol$
$\therefore 130\, kJ$ heat will decompose water $=\frac{1 \times 130}{260}$
$=0.5 \,mol$