Question

Given the following equations, calculate the ΔH of the reaction of ethylene gas (C2H4) with fluorine gas to make carbon tetrafluoride (CF4) gas and hydrogen fluoride gas. Show your work.
H2 (g) + F2 (g) → 2HF (g) ΔH = –537 kJ
C (s) + 2F2 (g) → CF4 (g) ΔH = –680 kJ
2C (s) + 2H2 (g) → C2H4 (g) ΔH = +52.3 kJ
Answer:

Answer 1

Answer is: the ΔH of the reaction is -2486.3 kJ.

Chemical reaction 1: H₂(g) + F₂(g) → 2HF(g) ΔH₁ = –537 kJ.

Chemical reaction 2: C(s) + 2F₂(g) → CF₄(g) ΔH₂ = –680 kJ.

Chemical reaction 3: 2C(s) + 2H₂(g) → C₂H₄(g) ΔH₃ = +52.3 kJ.

Chemical reaction 4: C₂H₄(g) + 6F₂(g) → 2CF₄(g) + 4HF(g) ΔH₄ = ?

Using Hess's law:

ΔH₄ = 2ΔH₁ + 2ΔH₂ - ΔH₃.

ΔH₄ = 2 · (-537 kJ) + 2 · (-680 kJ) - 52.3 kJ.

ΔH₄ = -2486.3 kJ.