Question

When $1\, g$ of anhydrous oxalic acid is burnt at $25^{\circ} C$, the amount of heat liberated is $2.835\, kJ . \Delta H$ combustion is (oxalic acid : $\left.C _{2} H _{2} O _{4}\right)$

• A. -255.15 kJ
• B. -445.65 kJ
• C. -295.24 kJ
• D. -155.16 kJ

Answer 1

Answer: (A)

$\underset{\text{(oxalic acid)}}{H_2C_2O_4(s)} + \frac{1}{2} O_2(g) \to 2CO_2 (g) + H_2O(l)$
We know,
$\Delta H _{\text {combusion }}=$ Amount of heat liberated when $1$ mole of substance reacts with oxygen.
Mol. wt. of oxalic acid $=90 \,g \,mol ^{-1}$
$1\,g$ oxalic acid liberates $2.835\, kJ$
$\therefore 90\, g$ ($1$ mole) oxalic acid liberates $2.835 \times 90\, kJ \,mol ^{-1}=255.15 \,kJ$
$\therefore $ Heat involved $=-255.15\, kJ$