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Question

If at 298 K, the bond energies of CH, CC, C=C and HH bonds are 414, 347, 615 and 435 kJ/mol respectively, then the value of enthalpy change for the reaction H2C=CH2(g)+H2(g)H3CCH3(g) at 298 K will be:


A
250 kJ
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B
+125 kJ
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C
125 kJ
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D
+250 kJ
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Solution

The correct option is C 125 kJ
Given that the bond energies of CH, CC, C=C and HH bonds are 414, 347, 615 and 435 kJ/mol respectively at 298 K.

We need to find the enthalpy change at 298 K for the following reaction: H2C=CH2(g)+H2(g)H3CCH3(g)

ΔH= Bond energy for reactants - Bond energy for products

ΔH=[4×(CH)+C=C+(HH)][6×(CH)+(CC)]

ΔH=[4×414+615+435][(6×414)+347]

ΔH=27062831

ΔH=125 kJ

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