Question

One mole of methanol when burnt in $O _{2}$, gives out $723\, kJ\, mol ^{-1}$ heat. If one mole of $O _{2}$ is used, what will be the amount of heat evolved?

• A. 723 kJ
• B. 924 kJ
• C. 482 kJ
• D. 241 kJ

Answer 1

Answer: (C)

$CH _{3} OH (l)+\frac{3}{2} O _{2}(g) \longrightarrow CO _{2}(g)+2 H _{2} O (l)$
$\Delta H=-723\, kJ$
By burning with $\frac{3}{2} O _{2}(g)$ heat evolved
$=-723\, kJ$
$\therefore $ By burning with $1$ mole $O _{2}(g) =\frac{-723 \times 2}{3}$
$=-482\, kJ$