Calculate the work done during combustion of $0.138 \mathrm{~kg}$ of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}_{(I)}$ at at $300 \mathrm{~K}$. Given : $R=8.314 J k^{-1} \mathrm{~mol}^{-1}$, molar mass of ethanol $=46 \mathrm{gmol}^{-1}$ (A) $-7482 J$ (B) $7482 J$ (C) $-2494 J$ (D) $2494 J$

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Calculate the work done during combustion of $0.138 \mathrm{~kg}$ of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}_{(I)}$ at at $300 \mathrm{~K}$ . Given : $R=8.314 J k^{-1} \mathrm{~mol}^{-1}$ , molar mass of ethanol $=46 \mathrm{gmol}^{-1}$ (A) $-7482 J$ (B) $7482 J$ (C) $-2494 J$ (D) $2494 J$

Chemistry

Calculate the work done during combustion of $0.138 \mathrm{~kg}$ of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}_{(I)}$ at at $300 \mathrm{~K}$ . Given : $R=8.314 J k^{-1} \mathrm{~mol}^{-1}$ , molar mass of ethanol $=46 \mathrm{gmol}^{-1}$ (A) $-7482 J$ (B) $7482 J$ (C) $-2494 J$ (D) $2494 J$

The correct option is B

Explanation:

The combustion of ethanol, involves the following reaction.
$C_{2} H_{5} O H(l)+3 O_{2}(g) \rightarrow 2 C O_{2}+3 H_{2} O$
Given,
Mass of ethanol $=0.138 \mathrm{~kg}=138 \mathrm{~g}$
Temperature $=300 K$
$R=8.314 J K^{-1} \mathrm{~mol}^{-1}$
Molar mass of ethanol $=46 \mathrm{~g} \mathrm{~mol}^{-1}$
No. of moles of ethanol $=\frac{\text { Mass of ethanol }}{\text { Molar mass of ethanol }}$
$=\frac{138}{46}=3$
Work done $(W)$ during combustion of $0138 \mathrm{~kg}$ of $C_{2} H_{5} O H=n R T$
$W=n R T$
$W=3 \times 8.314 J K^{-1} \mathrm{mor}^{-1} \times 300 K$
$W=7482.6 J$