Question

$1$ gram of hydrated oxalic acid $\left[( COOH )_{2} \cdot 2 H _{2} O \right]$ undergoes combustion it produces $2.2 \, kcal$ of heat. What will be its enthalpy of combustion ( $\Delta H_{c}$ )?

• A. $-2.2\,kcal$
• B. $-126\,kcal$
• C. $-277.2\,kcal$
• D. $-423\,kcal$

Answer 1

Answer: (C)

Combustion enthalpy is the amount of energy released during complete combustion of one mole of the reactant in the presence of the oxygen.

It is always negative as per the thermodynamic sign convention.

The molar mass of the hydrated oxalic acid is $=126\,g\,mol^{- 1}$

$1g \rightarrow -2.2\,kcal$

$126\,g \rightarrow -2.2\times 126\,kcal=-277.2\,kcal$