The standard molar heat of formation of ethane. CO2 and water are respectively -21.1, -94.1 and -68.3 kcal. The standard molar heat of combustion of ethane will be:

Question

The standard molar heat of formation of ethane. CO2 and water are respectively -21.1, -94.1 and -68.3 kcal. The standard molar heat of combustion of ethane will be: (A) - 372 kcal (B) 162 kcal (C) -240 kcal (D) 183.5 kcal

Tardigrade Admin · Accepted Answer

2 Use the following formula to find heat of combustion of
ethane.

Δ H^{o} = (Σ H_{f_{products}^{o}}) - (Σ H_{f_{reactants}}^{o})

Ethane undergoes combustion according to following reaction

C_{2} H_{6} (g) + \frac{7}{2} O_{2} (g) \to 2 C O_{2} (g) + 3 H_{2} O (g)

Given, heat of formation of ethane

= - 21.1 k c a l

Heat of formation of

C O_{2} = - 94.1 k c a l

Heat of formation of

H_{2} O = - 68.3 k c a l

Heat of formation of

O_{2} = 0

∴ H^{o} = [2 H_{f_{(C O_{2})}}^{o} + 3 H_{f_{(H_{2} O)}}^{o}] - [H_{f_{(C_{2} H_{6})}}^{o} + \frac{7}{2} H_{f_{(C O_{2})}}^{o}]

= [2 \times (- 94.1) + 3 \times (- 68.3)] - [- 2.11 + (7/2 \times 0)]

= (- 188.2 - 204.9) - (- 21.1) = - 393.1 + 21.1 = - 372 k c a l

Q. The standard molar heat of formation of ethane. CO2​ and water are respectively −21.1,−94.1 and -68.3kcal. The standard molar heat of combustion of ethane will be:

- 372 kcal

162 kcal

-240 kcal

183.5 kcal

Q. The standard molar heat of formation of ethane. $C O_{2}$ and water are respectively $- 21.1, - 94.1$ and - $68.3 k c a l$ . The standard molar heat of combustion of ethane will be: