Diketahui entalpi pembakaran 1 mol CH4 = -18 kkal, energi ikatan:
O = O = 119 kkal/mol
C = O = 173 kkal/mol
O – H = 110 kkal/mol
Maka energi ikatan C – H menjadi …
A. 6,75 kkal
B. 11,05 kkal
C. 33,13 kkal
D. 66,2 kkal
E. 132,5 kkal
Pembahasan
- ΔHreaksi = ΔHpemutusan – ΔHpembentukan
- -18 kkal = [4 (C – H) + 2(O = O)] – [2 (C = O) + 4 (O – H)]
- -18 kkal = [4 . (C – H) + 2 . 119 kkal/mol] – [2 . 173 kkal/mol + 4 . 110 kkal/mol]
- -18 kkal = [4 . (C – H) + 238 kkal/mol] – [786 kkal/mol]
- 4 (C – H) + 238 kkal/mol = (-18 + 786) kkal/mol = 768 kkal/mol
- 4 (C – H) = (768 – 238) kkal/mol = 530 kkal/mol
- (C – H) = 530/4 = 132,5 kkal
Soal ini jawabannya E.