Question

Can you give examples of exothermic reactions?

Answer 1

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

Explanation:

`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?