First slide

Enthalpy of Combustion

Question

Standard enthalpies of formation carbon dioxide, water and acetylene are $- 390, - 286 and + 254 kJ / mole$ respectively.
Enthalpy of combustion of acetylene is equal to…..kJ/mole

Moderate

A

-1410
B

-1530
C

-1260
D

-1320

Solution

Given,
$C (graphite) + O_{2} (g) \to {CO}_{2} (g), ∆ H = - 390 kJ / mole . . . . (1) H_{2} (g) + \frac{1}{2} O_{2} (g) \to H_{2} O_{} (l), ∆ H = - 286 kJ / mole . . . . (2) 2 C (graphite) + H_{2} (g) \to C_{2} H_{2} (g), ∆ H = + 254 kJ / mole . . . . (3) Required equation is C_{2} H_{2} (g) + \frac{5}{2} O_{2} (g) \to 2 {CO}_{2} (g) + H_{2} O (l) 2 \times Eq (1) + Eq (2) - Eq (3) = Required equation 2 (- 390) + (- 286) - (+ 254) = Required equation - 780 - 286 - 254 = Required equation ∆_{c}^{0} (C_{2} H_{2}) = - 1320 kJ / mole$

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