Question

# The standard heat of formation, ΔH∘f, is defined as the enthalpy change for the formation of...

The standard heat of formation, ΔH∘f, is defined as the enthalpy change for the formation of one mole of substance from its constituent elements in their standard states. Thus, elements in their standard states have ΔH∘f=0. Heat of formation values can be used to calculate the enthalpy change of any reaction.

Consider, for example, the reaction

2NO(g)+O2(g)⇌2NO2(g)

with heat of formation values given by the following table:

 Substance ΔH∘f (kJ/mol) NO(g) 90.2 O2(g) 0 NO2(g) 33.2

Then the heat of formation for the overall reaction is

ΔH∘rxn===ΔH∘f(products)2(33.2)−114 kJ/mol−−ΔH∘f(reactants)[2(90.2)+0]

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.

View Available Hint(s)

Check all that apply.

 Li(s)+12Cl2(l)→LiCl(s) Li(s)+12Cl2(g)→LiCl(s) SO3(g)→12O2(g)+SO2(g) SO(g)+12O2(g)→SO2(g) 2Li(s)+Cl2(g)→2LiCl(s) S(s)+O2(g)→SO2(g)

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 propane.

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