Chemical BondingHard

Question

Determine C-C & C-H bond enthalpy (in kJ/mol)
Given   ᐃfHo(C2H6, g) = - 85 kJ/mol
fHo(C3H8, g) = - 104 kJ mol
sublimation Ho (C, S) = 718 kJ/mol
Bond energy (H - H) = 436 kJ/mol

Options

A.414, 345
B.345, 414
C.287, 404.5
D.None of these

Solution

2C(s) + 3H2 → C2H6 (g)
fHo = [2 × ᐃSub 1 × (C, S) + 3 × B.E. (H-H)
- [B.E. (C - C) + 6 × BE (C - H)]
⇒ - 85 = 2 × 718 + 3 × 436 - (x + 6y)
x + 6y = 2829             ....(1)
Similarly for C3H8(g)
2x + 8y = 4002
x = 345, y = 414

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