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Heat of Formation

The standard ...

Question

The standard enthalpies of formation of $C O_{2} (g)$ , $H_{2} O (l)$ and glucose(s) at $25^{\circ} C$ are $- 400 k J / m o l$ , $- 300 k J / m o l$ and $- 1300 k J / m o l$ , respectively. The standard enthalpy of combustion per gram of glucose at $25^{\circ} C$ is

A

+ 2900 kJ

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B

−2900 kJ

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C

−16.11 kJ

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D

+16.11 kJ

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Solution

The correct option is C −16.11 kJ
The standard enthalpy of the combustion of glucose can be calculated by the equ.

$C_{6} H_{12} O_{6} (s) + 6 O_{2} (g) \to 6 C O_{2} (g) + 6 H_{2} O (l)$

$Δ H_{c} = 6 \times Δ H_{f} (C O_{2}) + 6 \times Δ H_{f} (H_{2} O) - Δ H_{f} [C_{6} H_{12} O_{6}]$

$Δ H^{0} = - \frac{2900}{180} = - 16.11 k J / g m$

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