Question

Calculate the standard enthalpy of formation of gaseous carbon tetrafluoride (CF₄) using the following thermochemical information:

Calculate the standard enthalpy of formation of gaseous carbon tetrafluoride (CF4) using the following thermochemical information: H2(g)F2(g) 2 HF(g) 2 CF4(g)4 HF(g) C2H4(g) +6 F2(g) C2H4(g)2 C(s) 2 H2(g) AH -537 kJ AH 2486.3 kJ AH -52.3 kJ ΔΗ - kJ

Answer 1

The formation reaction is:
C(s) + 2 F2(g) -> CF4(g)
Let this be reaction 0

Lets number the reaction as 0, 1, 2, 3 from top to bottom
required reaction should be written in terms of other reaction
This is Hess Law
required reaction can be written as:
reaction 0 = -1 * (reaction 1) -0.5 * (reaction 2) -0.5 * (reaction 3)

So, ΔHo rxn for required reaction will be:
ΔHo rxn = -1 * ΔHo rxn(reaction 1) -0.5 * ΔHo rxn(reaction 2) -0.5 * ΔHo rxn(reaction 3)
= -1 * (-537.0) -0.5 * (2486.3) -0.5 * (-52.3)
= -680 KJ
Answer: -680 KJ