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Heat of Formation

The heats of ...

Question

The heats of combustion of carbon, hydrogen and acetylene are $- 394 k J, - 286 k J$ and $- 1301 k J$ respectively. Calculate heat of formation of $C_{2} H_{2}$ .

A

621 k J

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B

454 k J

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C

- 227 k J

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D

227 k J

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Solution

The correct option is C $227 k J$
Solution:- (D) $227 k J$
Given:-
$C + O_{2} ⟶ C O_{2} Δ H = - 394 k J$
$2 \times [C + O_{2} ⟶ C O_{2} Δ H = - 394 k J]$
$2 C + 2 O_{2} ⟶ 2 C O_{2} Δ H = - 788 . . . . . (1)$
$H_{2} + \frac{1}{2} O_{2} ⟶ H_{2} O Δ H = - 286 k J . . . . . (2)$
$C_{2} H_{2} + \frac{5}{2} O_{2} ⟶ 2 C O_{2} + H_{2} O Δ H = - 1301 k J$
$2 C O_{2} + H_{2} O ⟶ C_{2} H_{2} + \frac{5}{2} O_{2} Δ H = 1301 k J . . . . . (3)$
Adding ${e q}^{n} (1), (2) & (3)$ , we have
$2 C + H_{2} ⟶ C_{2} H_{2} Δ H = 227 k J$
Hence the heat of formation of $C_{2} H_{2}$ is $227 k J$ .

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Similar questions

Q. The standard enthalpy of formation of octane

(C_{8} H_{18})

- 250 kJ/mol

. Calculate the enthalpy of combustion of

C_{8} H_{18}

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C O_{2} (g)

H_{2} O (l)

- 394 kJ/mol

- 286 kJ/mol

Q. The heats of formation of

C O_{2} (g)

H_{2} O (l)

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- 285.8 k J / m o l e

respectively. Using the data for the following combustion reaction, calculate the heat of formation of

C_{3} H_{8} (g)

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Q. Calculate the heat of formation of methane, given that
heat of formation of water

= - 286 k J {m o l}^{- 1}

heat of combustion of methane

= - 890 k J {m o l}^{- 1}

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Q. Given the following standard heats of reactions:
(a) heat of formation of water

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C_{2} H_{2} = - 310.6 k c a l

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25^{o} C

2 C (s) + 2 O_{2} (g) ⟶ 2 C O_{2} (g); Δ H = - 787 k J . . . (i)

H_{2} (g) + \frac{1}{2} O_{2} (g) ⟶ H_{2} O (l); Δ H = - 286 k J . . . (i i)

C_{2} H_{2} (g) + \frac{5}{2} O_{2} (g) ⟶ 2 C O_{2} (g) + 3 H_{2} O (l) . . . . (i i i)

Δ H = - 1301 k J

Heat formation of acetylene is:

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