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Standard XII

Chemistry

Thermodynamic Processes

Heats of form...

Question

Heats of formation of SiO $_{2}$ and MgO are -48.24 and -34.7 KJ respectively. The heat of the reaction: $2 M g + S i O_{2} \to 2 M g O + S i$ is

21.64 KJ

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-21.16 KJ

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-13.62 KJ

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13.62 KJ

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Solution

The correct option is A -21.16 KJ
(i) $S i + O_{2} \to S i O_{2}, Δ H = - 48.24$
(ii) $M g + \frac{1}{2} O_{2} \to M g O, Δ H = - 34.7$
$2 \times (i i) - (i)$ gives, $2 M g + S i O_{2} \to 2 M g O + S i$
$Δ H = - 34.7 \times 2 + 48.24 = - 21.16 K J .$

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Heats of formation of SiO2 and MgO are -48.24 and -34.7 KJ respectively. The heat of the reaction: 2Mg+SiO2→2MgO+Si is

The correct option is A -21.16 KJ(i) Si+O2→SiO2,ΔH=−48.24(ii) Mg+12O2→MgO,ΔH=−34.72×(ii)−(i) gives, 2Mg+SiO2→2MgO+SiΔH=−34.7×2+48.24=−21.16KJ.

Heats of formation of SiO $_{2}$ and MgO are -48.24 and -34.7 KJ respectively. The heat of the reaction: $2 M g + S i O_{2} \to 2 M g O + S i$ is

The correct option is A -21.16 KJ
(i) $S i + O_{2} \to S i O_{2}, Δ H = - 48.24$
(ii) $M g + \frac{1}{2} O_{2} \to M g O, Δ H = - 34.7$
$2 \times (i i) - (i)$ gives, $2 M g + S i O_{2} \to 2 M g O + S i$
$Δ H = - 34.7 \times 2 + 48.24 = - 21.16 K J .$