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Heat of Formation

The heat of c...

Question

The heat of combustion of liquid ethanol is $- 327.0 k c a l$ . Calculate the heat of formation of ethanol, given that the heats of formation of $C O_{2} (g)$ and $H_{2} O (l)$ are $- 94.0 k c a l$ and $- 68.4 k c a l$ respectively.

A

36.2 k c a l

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B

- 36.2 k c a l

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C

- 66.2 k c a l

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D

66.2 k c a l

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Solution

The correct option is B $- 66.2 k c a l$
Heat of formation of ethanol = 2 $\times$ heat of formation of $C O_{2}$ + 3 $\times$ heat of formation of water - heat of combustion of ethanol
Heat of formation of ethanol = $2 * (- 94) + 3 * (- 68.4) - (- 327)$ = $- 66.2 k c a l$

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