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Heat of Formation

At 300K, the ...

Question

At 300K, the standard enthalpies of formation of $C_{6} H_{5} C O O H_{(s)}, C O_{2 (g)},$ and $H_{2} O_{(l)}$ are -408, -393 and -286 kJ mol respectively. Calculate the heat of combination of benzoic acid at constant volume.

A

+3201 kJ

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B

+3199.75 kJ

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C

-3201 kJ

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D

-3199.75 kJ

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Solution

The correct option is B +3199.75 kJ
$C_{6} H_{5} C O O H + \frac{15}{2} H_{2} O ⟶ 7 C O_{2} + 3 H_{2} O$
According to the following combustion reaction:
$Δ H_{c o m b u s t i o n}$ of $C_{6} H_{5} C O O H = (Δ H_{f o r m a t i o n}$ of $C_{6} H_{5} C O O H) - 7 (Δ H_{f o r m a t i o n}$ of $C O_{2}) - 3 (Δ H_{f o r m a t i o n}$ of $H_{2} O)$
$= - 408 - 7 (393) - 3 (- 286) = + 3199.75$ kJ

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Similar questions

300

K the standard enthalpies of formation of

C_{6} H_{5} C O O H_{(s)}, C O_{2 (g)}

H_{2} O_{(l)}

- 408, - 393

- 286

m o l^{- 1}

respectively. Calculate the heat of combustion of benzoic acid at constant volume.

Q. At 300 K , the standard enthalpies of formation of

C_{6} H_{5} C O O H (s)

C O_{2} (g)

H_{2} O (l)

are ; -408, -393 , & -286 kJ mol respectively.
Calculate the heat of combustion of benzoic acid at:
(i) constant pressure
(ii) constant value

Q. The standard enthalpy of formation of octane

(C_{8} H_{18})

- 250 k J / m o l

. Calculate the enthalpy of combustion of

C_{8} H_{18}

.
Given : enthalpy of formation of

C O_{2} (g)

H_{2} O (l)

- 394 k J / m o l

- 286 k J / m o l

300 K

, the standard enthalpies of formation of

C_{6} H_{5} C O O H (s), C O_{2} (g)

H_{2} O (l)

- 408, - 393

- 286

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

respectively. Calculate the heat of combustion of benzoic acid at (i) constant pressure and (ii) constant volume.

(R = 8.31 J {m o l}^{- 1} K^{- 1})

Q. Calculate the standard enthalpy of formation of

C H_{3} O H (l)

from the following data.

C H_{3} O H (l) + \frac{3}{2} O_{2} (g) \to C O_{2} (g) + 2 H_{2} O (l)

Δ H^{o} = - 726

m o l^{- 1}

+ O_{2} (g) \to C O_{2} (g);

Δ_{c} H^{0} = - 393

m o l^{- 1}

H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l);

Δ_{t} H^{o} = - 286

m o l^{- 1}

.

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