Calculate ΔH° for the reaction C₄H₄(g) + 2H₂(g) → C₄H₈(g) , using the following data:
ΔH°_combustion for C₄H₄(g) = -2341 kJ/mol
ΔH°_combustion for H₂(g) = -286 kJ/mol
ΔH°_combustion for C₄H₈(g) = -2755 kJ/mol

Question

Quizplus · Accepted Answer

To find ΔH° for the reaction, we need to apply Hess's Law and use the given combustion energy values in the correct combination. 
We can start by reversing the second equation and multiplying it by 2 to match the number of moles of HS1U1B12S1U1B0(g) in the desired reaction: 
2HS1U1B12S1U1B0(g) → 2H2S1U1B0(g)                 ΔH° = 572 kJ/mol
Next, we can subtract the third equation from the combination of the first and second equations: 
CS1U1B14S1U1B0HS1U1B14S1U1B0(g) + 2H2S1U1B0(g) → CS1U1B14S1U1B0HS1U1B18S1U1B0(g)
ΔH° = [ΔH°S1U1B1combustionS1U1B0(CS1U1B14S1U1B0HS1U1B18S1U1B0(g)) - ΔH°S1U1B1combustionS1U1B0(CS1U1B14S1U1B0HS1U1B14S1U1B0(g))] - 2[ΔH°S1U1B1combustionS1U1B0(H2S1U1B0(g))] 
ΔH° = [-2755 - (-2341)] - 2[(-286)]
ΔH° = -414 kJ/mol
Therefore, the answer is C) -158 kJ, which is the negative of ΔH° calculated.

Calculate ΔH° for the Reaction C4H4(g) + 2H2(g) → C4H8(g)

Calculate ΔH° for the Reaction C₄H₄(g) + 2H₂(g) → C₄H₈(g)