For which of the following reactions is ΔH∘rxnΔHrxn∘ equal to ΔH∘fΔHf∘ of the product(s)?You do not need to look up any values to answer this question. C(s,graphite)+O2(g)→CO2(g)C(s,graphite)+O2(g)→CO2(g) Na(s)+12F2(l)→NaF(s)Na(s)+12F2(l)→NaF(s) CO(g)+12O2(g)→CO2(g)CO(g)+12O2(g)→CO2(g) 2Na(s)+F2(g)→2NaF(s)2Na(s)+F2(g)→2NaF(s) BaCO3(s)→BaO(s)+CO2(g)BaCO3(s)→BaO(s)+CO2(g) Na(s)+12F2(g)→NaF(s)
The standard heat of formation, ΔH∘fΔHf∘, 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=0ΔHf∘=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)2NO(g)+O2(g)⇌2NO2(g)
with heat of formation values given by the following table:
| Substance | ΔH∘fΔHf∘ (kJ/molkJ/mol) |
| NO(g)NO(g) | 90.2 |
| O2(g)O2(g) | 0 |
| NO2(g)NO2(g) | 33.2 |
Then the standard heat of reaction for the overall reaction is
ΔH∘rxn===ΔH∘f(products)2(33.2)−114 kJ−−ΔH∘f(reactants)[2(90.2)+0]
For which of the following reactions is ΔH∘rxnΔHrxn∘ equal to ΔH∘fΔHf∘ of the product(s)?You do not need to look up any values to answer this question.
| C(s,graphite)+O2(g)→CO2(g)C(s,graphite)+O2(g)→CO2(g) |
| Na(s)+12F2(l)→NaF(s)Na(s)+12F2(l)→NaF(s) |
| CO(g)+12O2(g)→CO2(g)CO(g)+12O2(g)→CO2(g) |
| 2Na(s)+F2(g)→2NaF(s)2Na(s)+F2(g)→2NaF(s) |
| BaCO3(s)→BaO(s)+CO2(g)BaCO3(s)→BaO(s)+CO2(g) |
| Na(s)+12F2(g)→NaF(s) |
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