Question

When a certain amount of ethylene was combusted, $6226\text{kJ}$ heat was evolved. If heat of combustion of $1$ mole of ethylene is $1411\text{kJ}$, the volume of $O_2$ (at NTP) that entered into the reaction is:

• A. $296.5\text{mL}$
• B. $296.5\text{litres}$
• C. $6226\times 22.4\text{litres}$
• D. $22.4\text{litres}$

Answer 1

The correct option is B $296.5\text{litres}$

Reaction of Combustion of ethylene is:
$C_2{H}_4+3O_2\to 2C{O}_2+2H_{2}O;\Delta H_{\text{comb.}}=1411\text{kJ}$
This $\Delta H_{\text{comb.}}$ is when we have $n_{C_2{H}_4}=1\text{mol}$ or $n_{O_2}=3\text{mol}$, where $n$ represents the number of moles.
So, when $\Delta H_{\text{comb.}}=6226\text{kJ}$
Then moles of oxygen, $n_{O_2}=\left(\frac{6226}{1411}\right)\times 3\text{mol}$

Since the process is taking place at NTP, so the volume of oxygen consumed $=n_{O_2}\times \text{molar volume}$
$=\left(\frac{6226\times 3}{1411}\right)\times 22.4\because \text{molar volume}=22.4\text{L}=296.5\text{L}$