Calculate the enthalpy change (△H) of the following reaction 2C2H2(g)+5O2(g)→4CO2(g)+2H2O(g) given average bond enthalpies of various bonds, i.e., C−H,C≡C,O=O,C=O,O−H as 414, 814 499, 724 and 640 kJmol−1 respectively.
A
−2600kJmol−1
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B
+2573kJmol−1
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C
−2573kJmol−1
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D
+2600kJmol−1
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Solution
The correct option is C−2573kJmol−1 Given- Bond enthalpies of various bonds εC−H=414kJmol−1 εC≡C=814kJmol−1 εO=O=499kJmol−1 εC=O=724kJmol−1 εO−H=640kJmol−1 △Hf=2[εC≡C+2εC−H]+5εO=O−4[2εC=O]−2[2εO−H] △Hf=2[814+2×414]+5[499]−[8×724]−4[640] =3284+2495−5792−2560=−2573kJ/mol. hence, △Hf=−2573kJ/mol.