Given the following equations, calculate the ΔH of reaction of ethylene gas (C2H4) with fluorine gas to make carbon tetrafluoride (CF4) gas and hydrogen fluoride gas. Show your work.

Question

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 1

Reverse eqn 3, and add 2x eqn 2 and 2x eqn 1 to get
C2H4 + 6F2 ==> 2CF4 + 4HF