Question

When $1.0g$ of oxalic acid ($H_2{C}_2{O}_4)$ is burned in a bomb calorimeter whose heat capacity is $8.75kJ/K$, the temperature increased by $0.312K$. The enthalpy of combustion of oxalic acid at ${27}^{\circ }C$.

• A. -245.7 kJ/mol
• B. -244.452 kJ/mol
• C. 241.95 kJ/mol
• D. -58.85 kJ/mol

Answer 1

The correct option is C

241.95 kJ/mol

Heat of combustion of oxalic acid at const vol ($\Delta U$)

Heat evolved by the combustion of 1 gr of $H_2{O}_2{O}_4$ = $S\times \Delta T$ = $8.75\times 0.312=2.73kJ$

Heat evolved by the combustion of 90 gr oxalic acid = $2.73\times 90$ = $245.7$

$\therefore$ Heat of combustion of $H_2{C}_2{O}_4$ at const vol $\left(\Delta U\right)$ = $-245.7$

The combustion eq. For the reaction is

$H_1{C}_2{O}_4+\frac{1}{2}{O}_2\to 2C{O}_2+H_{2}O$

$\left(s\right)\left(g\right)\left(g\right)\left(s\right)$

$\Delta n=\frac{3}{2}$

$\Delta H=\Delta U+\Delta nRT=245.7+\frac{3}{2}\times 8.314\times 300\times {10}^{-3}$

= $241.95kJ/mol$