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Resonance Effect

An organic mo...

Question

An organic molecule has $5$ C $=$ C bonds (heat of hydrogenation for C $=$ C bond is $28.8$ kJ $m o l^{- 1}$ ) at experiment value for heat of hydrogenation is $99$ kJ $m o l^{- 1}$ . The resonance energy in kJ $m o l^{- 1}$ is?

A

45

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B

90

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C

70

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D

140

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Solution

The correct option is B $45$
Resonance energy $=$ Theoretical Heat of Hydrogenation $-$ Experimental Heat of Hydrogenation
$= (5 \times 28.8) - 99$
$= 45 K J / m o l$

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Similar questions

Q. The bond energies of

C - C, C = C, H - H

C - H

350, 600, 400

410 kJ/mol

respectively. The heat of hydrogenation of ethylene is:

Q. Calculate the resonance energy of

C_{6} H_{6}

, using Kekule formula for

C_{6} H_{6}

from the following data: (i)

Δ H^{\circ}

C_{6} H_{6} = - 358.5 k J m o l^{- 1}

H e a t o f a t o m i s a t i o n o f C = 716.8 k J m o l^{- 1}

(iii) Bond energy of

C - - H, C - - C, C = = C

H - - H

are 490, 340, 620 and

436.9 k J m o l^{- 1}

. Report your answer in kj (only value).

Q. Using the data provided, calculate the multiple bond energy

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

C \equiv C

C_{2} H_{2} .

Given that the heat of formation of

C_{2} H_{2} = 225 k J m o l^{- 1} .

(take the bond energy of

C - H

350 k J m o l^{- 1}

2 C (s) \to 2 C (g) △ H = 1410 k J m o l^{- 1}

H_{2} (g) \to 2 H (g) △ H = 330 k J m o l^{- 1}

Q. The standard molar enthalpies of hydrogenation of benzene (

l

25^{o} C

- 208 {kJ mol}^{- 1}

. The standard enthalpy of hydrogenation of cyclohexene

(l)

25^{o} C

- 119 {kJ mol}^{- 1}

. Use these data to estimate the magnitude of the resonance energy of benzene.
(correct answer +1, wrong answer -0.25)

Δ_{f} H^{⊖}

(l)

25^{\circ} C

- 156

+ 46 k J m o l^{- 1}

, respectively.

Δ_{h y d r o g e n a t i o n} H^{⊖}

(l)

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

.
Resonance energy of benzene is found to be

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

. Find the value of x.

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