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  4. One mole of methanol, when burnt in oxygen, gives out 723 kJ mol- 1 heat. If one mole of oxygen is used, what will be the amount of heat evolved?

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

NTA AbhyasNTA Abhyas 2022

Solution:

$\underset{2 m o l}{2 C H_{3} O H}+\underset{3 m o l}{3 O_{2}} \rightarrow 2CO_{2}+4H_{2}O$
$\Delta H=-723kJ/mol$
1 mol $O_{2}\equiv \frac{2}{3}molCH_{3}OH$
1 mol $CH_{3}OH$ on combustion gives out 723 kJ heat
So $\frac{2}{3}molCH_{3}OH$ combustion gives out $=723\times \frac{2}{3}$ kJ heat
$=482$ kJ heat.