Question

For which of the following reactions is Δ H ∘ rxn equal to Δ H ∘ f of the product(s)? You do not need to look up any values to answer this question. Check all that apply. Check all that apply. BaC O 3 (s)→BaO(s)+C O 2 (g) C(s,graphite)+ O 2 (g)→C O 2 (g) CO(g)+ 1 2 O 2 (g)→C O 2 (g) 2Na(s)+ F 2 (g)→2NaF(s) Na(s)+ 1 2 F 2 (l)→NaF(s) Na(s)+ 1 2 F 2 (g)→NaF(s) Part B The combustion of propane, C 3 H 8 , occurs via the reaction C 3 H 8 (g)+5 O 2 (g)→3C O 2 (g)+4 H 2 O(g) with heat of formation values given by the following table: Substance Δ H ∘ f ( kJ/mol ) C 3 H 8 (g) -104.7 C O 2 (g) − 393.5 H 2 O(g) − 241.8 Calculate the enthalpy for the combustion of 1 mole of propane. Express your answer to four significant figures and include the appropriate units.

Answer 1

C(s,graphite)+ O 2 (g)→C O 2 (g)

Hrex   = Hf products - Hf reactants

Hrex    = Hrex products

             = -393.5 -(0+0)

            - -393.5KJ/mole

Na(s)+ 1 2 F 2 (g)→NaF(s)

Hrex = Hf rpoducts

2Na(s)+ F 2 (g)→2NaF(s)

Hrex = Hf rpoducts

Na(s)+ 1 2 F 2 (l)→NaF(s)

Hrex = Hf rpoducts

C 3 H 8 (g)+5 O 2 (g)→3C O 2 (g)+4 H 2 O(g)

Hrex   = Hf products - Hf reactants

               = 3*-393.5 +4*-241.8-(-104.7) = -2043KJ/mole