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Standard XII

Chemistry

Properties of Enthalpy

Using bond en...

Question

Using bond energy data, calculate heat of formation of isoprene 5C(s) + 4H2(g) → H2C=C(CH3)-CH=CH2 Given C-H, H-H, C-C, C=C and C(s)→ C(g) respectively as 98.8 kcal, 104 kcal,83kcal,147 kcal, 171 kcal

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Q. Estimate the heat of formation of gaseous isoprene

(H_{2} C = C H_{3} | c - H | C = C H_{2})

from the following data;

Bond energies:

C - H

= 98.8 kcal/mole

H - H

= 104.0 kcal/mole

C - C

= 83.1 kcal/mole

C = C

= 147.0 kcal/moleHeat of sublimation of carbon (s) = 171.7 kcal per mole

Calculate the enthalpy of the following reaction. $H_{2} C = C H_{2} (g) + H_{2} (g) \to C H_{3} - C H_{3} (g)$

The bond energies of C - H, C - C, C = C & H - H are 99, 83, 147 & 104 Kcal respectively.

Q. The enthalpy of formation of isoprene is
(Neglect resonance in isoprene)
Given :

C - H = 98.8

k Cal ;

H - H = 104

k Cal;

C - C = 83

k Cal;

C = C = 147

k Cal &

C (s) \to C (g) = 171

k Cal.

Δ H_{f}

C_{2} H_{4} = 12.5 k c a l

Heat of atomisation of

C = 171 k c a l

. Bond energy of

H_{2} = 104.3 k c a l

. Bond energy

C - H = 99.3 k c a l

. What is

C = C

bond energy?

Q. The heat of combustion of acetylene is 312 kcal. If heat of formation of

C O_{2}

and

H_{2} O

are 94.38 and 68.38 kcal respectively,

C \equiv \equiv C

bond energy is

x k c a l

. Given that heat of atomisation of C and H are 150.0 and 51.5 kcal respectively and

C - - H

bond energy is 93.64 kcal. Value of

x

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