Q15 / 150 · MHT CET 2011 · Chemistry

The heat of combustion of carbon is $-393.5 \mathrm{~kJ} / \mathrm{mol}$. The heat released upon the formation of $35.2 \mathrm{~g}$ of $\mathrm{CO}_{2}$ from carbon and oxygen gas is

  • A
    $+315 \mathrm{~kJ}$
  • B
    $-31.5 \mathrm{~kJ}$
  • Correct answer
    C
    $-315 \mathrm{~kJ}$
  • D
    $+31.5 \mathrm{~kJ}$

Solution

$$ \begin{aligned} \mathrm{C}+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2} & \\ & \Delta H=-393.5 \mathrm{~kJ} / \mathrm{mol} \end{aligned} $$ Heat released upon the formation of $44 \mathrm{~g}$ of $$ \mathrm{CO}_{2}=-393.5 \mathrm{~kJ} $$ $\therefore$ Heat released upon the formation of $1 \mathrm{~g}$ of $$ \mathrm{CO}_{2}=\frac{-393.5}{44} \mathrm{~kJ} $$ $\therefore$ Heat released upon the formation of $35.2 \mathrm{~g}$ of $$ \begin{aligned} \mathrm{CO}_{2} &=\frac{-393.5}{44} \times 35.2 \\ & \simeq-315 \mathrm{~kJ} \end{aligned} $$

Hence, the correct answer is option: 'C'.

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