Question

Calculate ΔH_rxn for the reaction:

5C (s) + 6 H₂ (g) → C₅H₁₂(l)

Use the following reaction:

C₅H₁₂(l) + 8O₂(g) → 5CO₂(g) + 6H₂O(g) ΔH = -3244.8 kJ

And use the formation reactions for carbon dioxide gas and gaseous water as seen in your handout.
Handout values: [CO₂ (g) ΔH = -393.5], [H₂O (g) ΔH = -241.8]

Answer 1

C₅H₁₂(l) + 8O₂(g) → 5CO₂(g) + 6H₂O(g) ΔH = -3244.8 kJ

ΔHrxn   = ΔHf products - ΔHf reactants

   -3244.8    = 5*ΔHf CO2 + 6*ΔHf -ΔHf C5H12

     -3244.8   = 5*-393.5+6*-241.8-ΔHf C5H12

   -3244.8    = -3418.3-ΔHf C5H12

-ΔHf C5H12    = -3244.8+3418.3

ΔHf C5H12    = -173.5Kj

5C (s) + 6 H₂ (g) → C₅H₁₂(l)

ΔHrxn   = ΔHf products - ΔHf reactants

              =ΔHf C5H12- 5*ΔHf C - 6*ΔHf H2

              = -173.5 -5*0 -6*0

              = -173.5KJ >>>>>>answer