Calculate the enthalpy for the combustion of 1 mole of heptane?

NetherCraft 0

The combustion of heptane, C7H16, occurs via the reaction:

C7H16(g)+11O2(g)→7CO2(g)+8H2O(g)

with heat of formation values given by the following table:

Substance ΔH∘f

(kJ/mol)

C7H16 (g) -187.9

CO2(g) −393.5

H2O(g) −241.8

Calculate the enthalpy for the combustion of 1 mole of heptane. Express your answer to four significant figures and include the appropriate units.

2 Answers

  • products − reactants:

    All units in kJ/mol:

    (7 x −393.5) + (8 x −241.8) − (−187.9) − (11 x 0) = −4501 kJ/mol C7H16

  • Almost, remember that you multiplied the standard heat values (kJ/mole) of the substances by the number of moles of the respective substance. In the end, the moles cancel.

    (7 moles x −393.5 kJ/mole) + (8 moles x −241.8 kJ/mole) − (1 mole x −187.9 kJ/mole) − (11 moles x 0 kJ/mole) = −4501 kJ C7H16

    So, the resulting energy should be in kJ, not kJ/mole.

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