If enthalpies of formation for C 2 H 4 ( g ) , CO 2 ( g ) and H 2 O ( ℓ ) at 2 5 ∘ C and 1 atm , pressure are 52 , − 394 and 286 KJ / mol respectively, then enthalpy of combustion of C 2 H 4

Question

If enthalpies of formation for C 2 ​ H 4 ​ ( g ) , CO 2 ​ ( g ) and H 2 ​ O ( ℓ ) at 2 5 ∘ C and 1 atm , pressure are 52 , − 394 and 286 KJ / mol respectively, then enthalpy of combustion of C 2 ​ H 4 ​ ( g ) will be

TestHub · Accepted Answer

Question Explanation:

Calculate the enthalpy of combustion of ethene from the enthalpies of formation of ethene, CO , and

water.

Concept:

This question is based on enthalpy of combustion.

Solution:

The combustion reaction for ethene is:

C₂H₄(g) + 3O₂(g) → 2CO₂(g) + 2H₂O(l)

$Δ H^{\circ} = [2 \times (Δ H_{f}^{\circ})_{C O_{2}} + 2 \times (Δ H_{f}^{\circ})_{H_{2} O}] - [(Δ H_{f}^{\circ})_{C_{2} H_{4}} + 3 \times (Δ H_{f}^{\circ})_{O_{2}}]$

$Δ H^{\circ} = [2 \times (- 394) + 2 \times (- 286)] - [52 + 3 \times 0]$

$Δ H^{\circ} = [- 788 - 572] - [52]$

$Δ H^{\circ} = - 1360 - 52$

$Δ H^{\circ} = - 1412 k J / m o l$

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