2
Question
Using the data provided, calculate the multiple bond energy (kJ mol−1) of a C≡C bond in C2H2. Given that the heat of formation of C2H2=225 kJ mol−1. (take the bond energy of C−H bond as 350 kJ mol−1 ):
2C(s)→2C(g) △H=1410 kJ mol−1
H2(g)→2H(g) △H=330 kJ mol−1
Using the data provided, calculate the multiple bond energy (kJ mol−1) of a C≡C bond in C2H2. Given that the heat of formation of C2H2=225 kJ mol−1. (take the bond energy of C−H bond as 350 kJ mol−1 ):
2C(s)→2C(g) △H=1410 kJ mol−1
H2(g)→2H(g) △H=330 kJ mol−1
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Solution
The correct option is D 815
(i) 2C(s)+H2(g)→H−C≡C−H(g) △Hf=225 kJ mol−1
(ii) 2C(s)→2C(g) △H=1410 kJ mol−1
(iii) H2(g)→2H(g) △H=330 kJ mol−1
From equation (i):
ΔHf=[ΔHsub+ΔH ]−[2×BEC−H+1×eC≡C]
225=[1410+1×330]−[2×350+1×BEC≡C]
225=[1410+330]−[700−BEC≡C]
225=1740−700−BEC≡C
BEC≡C=1040−225=815 kJ mol−1
BEC≡C=815 kJ mol−1
(i) 2C(s)+H2(g)→H−C≡C−H(g) △Hf=225 kJ mol−1
(ii) 2C(s)→2C(g) △H=1410 kJ mol−1
(iii) H2(g)→2H(g) △H=330 kJ mol−1
From equation (i):
ΔHf=[ΔHsub+ΔH ]−[2×BEC−H+1×eC≡C]
225=[1410+1×330]−[2×350+1×BEC≡C]
225=[1410+330]−[700−BEC≡C]
225=1740−700−BEC≡C
BEC≡C=1040−225=815 kJ mol−1
BEC≡C=815 kJ mol−1
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