Can you give examples of exothermic reactions?

1 Answer
Feb 12, 2017

An example of an exothermic reaction is provided by the combustion of a hydrocarbon:


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

The extensively measured enthalpy change for this reaction is, #DeltaH_f^@=-890.2*kJ*mol^-1#. This means that so much energy is released per mole of reaction as written.

Given the sign on #DeltaH_f^@#, we could write the reaction in the following terms:

#CH_4(g) +2O_2(g) rarr CO_2(g) + 2H_2O +890.2*kJ#

Because the enthalpy difference represents the difference between bonds made (energy out) and bonds broken (energy in), we can thus use enthalpy as a virtual product in the reaction, with the appropriate 1:1 molar relationship with the methane that is combusted. Are you happy with this?