Question

Part A

For which of the following reactions is ΔH∘rxn equal to ΔH∘f of the product(s)?

You do not need to look up any values to answer this question.

Check all that apply.

Hints

Check all that apply.

S(s)+O2(g)→SO2(g)

Li(s)+12F2(g)→LiF(s)

SO(g)+12O2(g)→SO2(g)

SO3(g)→12O2(g)+SO2(g)

2Li(s)+F2(g)→2LiF(s)

Li(s)+12F2(l)→LiF(s)

Part B

The combustion of propane, C3H8, occurs via the reaction

C3H8(g)+5O2(g)→3CO2(g)+4H2O(g)

with heat of formation values given by the following table:

Substance	ΔH∘f (kJ/mol)
C3H8 (g)	-104.7
CO2(g)	−393.5
H2O(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

Part A: enthalpy of reactions = formation enthalpy of products - formation enthalpy of reactants

criteria: enthalpy of formation of any element (solid, liquid, gas state) is zero

so, enthalpy of reactions = formation enthalpy of products for following reactions

S(s)+O2(g)→SO2(g)

Li(s)+12F2(g)→LiF(s)

2Li(s)+F2(g)→2LiF(s)

Li(s)+12F2(l)→LiF(s)

Part B:

enthalpy of combustion = formation enthalpy of products - formation enthalpy of reactants

= [3*(−393.5) + 4*(−241.8) - (-104.7 + 0) ] kj/mole

= - 2043 kj/mole