Calculate the enthalpy of combustion of methane,if the standard enthalpies of formation of methane, carbon dioxide, water are -74.85,-393.5 and -286?

1 Answer
anor277
Feb 4, 2018

#DeltaH_"combustion"^@=-890.7*kJ*mol^-1#

Explanation:

We want the enthalpy associated with the combustion reaction...

#CH_4(g) +O_2(g) rarr CO_2(g) + 2H_2O(l)+Delta_"rxn"#

Now it is a fact that....

#DeltaH_"rxn"^@=SigmaDeltaH_f^@"(products)"-SigmaDeltaH_f^@"(reactants)"#

And we have been given the appropriate data...

#DeltaH_"rxn"^@={(-393.5-2xx286)-(-74.85)}*kJ*mol^-1#

#=-890.7*kJ*mol^-1#

When you do these things you have to be mindful of the sign conventions, i.e. #-(-)=+#... And when we write #mol^-1#, we mean #"per mole of reaction as written..."# Capisce?

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