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Limitations of First Law

The heat of f...

Question

The heat of formation of $C_{2} H_{5} O H (l)$ is $- 66 k c a l m o l^{- 1}$ . The heat of combustion of $C H_{3} O C H_{3} (g)$ is $- 348 k c a l m o l^{- 1}$ . $△ H_{f}$ for $H_{2} O$ and $C O_{2}$ are $- 68 k c a l m o l^{- 1}$ and $- 94 k c a l m o l^{- 1}$ respectively.
Then, the $△ H$ for reaction $C_{2} H_{5} O H (l) \to C H_{3} O C H_{3} (g)$ is :

A

△ H = 18 k c a l m o l^{- 1}

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B

△ H = 22 k c a l m o l^{- 1}

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C

△ H = 26 k c a l m o l^{- 1}

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D

△ H = 30 k c a l m o l^{- 1}

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Solution

The correct option is B $△ H = 22 k c a l m o l^{- 1}$
$△ H_{f}^{o} C_{2} H_{5} O H (l) = - 66 k c a l / m o l$
$2 C (s) + \frac{1}{2} O_{2} (g) + 3 H_{2} (g) \to C_{2} H_{5} O H (l)$
$△ H_{1} = - 66 k c a l m o l^{- 1}$ ....(1)

$C H_{3} - O - C H_{3} (g) + 3 O_{2} (g) \to 2 C O_{2} (g) + 3 H_{2} O (l) △ H_{2} = - 348 k c a l m o l^{- 1}$ ...(2)

$H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O (l) △ H_{3} = - 68 k c a l m o l^{- 1}$ ...(3)

$C (s) + O_{2} (g) \to C O_{2} (g) △ H_{4} = - 94 k c a l m o l^{- 1}$ ....(4)

Then for reaction,
$C_{2} H_{5} O H (l) \to C H_{3} O C H_{3} (g)$

This reaction can be obtained by the combination,
Target equation = - eq.(1) - eq.(2) + 3 [eq.(3)] + 2 [eq.(4)]
So, $△ H$ for the above isomerisation reaction can be obtained by ;

$△ H = + 66 + 348 - 3 \times 68 - 2 \times 94 = + 66 + 348 - 204 - 188$

$\Rightarrow △ H = 22 k c a l m o l^{- 1}$

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Similar questions

Q. The heat of formation of

C_{2} H_{5} O H (l)

- 66 k c a l m o l^{- 1}

. The heat of combustion of

C H_{3} O C H_{3} (g)

- 348 k c a l m o l^{- 1}

△ H_{f}

H_{2} O

C O_{2}

- 68 k c a l m o l^{- 1}

- 94 k c a l m o l^{- 1}

respectively.
Then, the

△ H

C_{2} H_{5} O H (l) \to C H_{3} O C H_{3} (g)

Q. The heat of formation of

C_{2} H_{5} O H (l)

- 66 k c a l m o l^{- 1}

. The heat of combustion of

C H_{3} O C H_{3} (g)

- 348 k c a l m o l^{- 1}

△ H_{f}

H_{2} O

C O_{2}

- 68 k c a l m o l^{- 1}

- 94 k c a l m o l^{- 1}

respectively.
Then, the

△ H

for the reaction

C_{2} H_{5} O H (l) \to C H_{3} O C H_{3} (g)

Q. The heat of formation of

C_{2} H_{5} O H (l)

- 66 k c a l m o l^{- 1}

. The heat of combustion of

C H_{3} O C H_{3} (g)

- 348 k c a l m o l^{- 1}

△ H_{f}

H_{2} O

C O_{2}

- 68 k c a l m o l^{- 1}

- 94 k c a l m o l^{- 1}

respectively.
Then, the

△ H

C_{2} H_{5} O H (l) \to C H_{3} O C H_{3} (g)

Q. The heat of formation of

C_{2} H_{5} O H (l)

is -66 kcal/mole. The heat of combustion of

C H_{3} O C H_{3} (g)

is -348 kcal mole,

Δ H_{f}

H_{2} O

C O_{2}

are - 68 kcal/mole and -94 kcal/mole respectively. Then determine the

Δ H

for the isomerisation reaction

C_{2} H_{5} O C H_{3} (g)

Δ E

for the same are at T = 25

^{\circ}

C

Q. Bond dissociation energy of

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103 k c a l m o l^{- 1}

and heat of formation of

C H_{4} (g)

- 17.88 k c a l m o l^{- 1} .

The dissociation energy of

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103 k c a l / m o l .

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Limitations of First Law

Standard XII Chemistry

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