Can you give examples of exothermic reactions?
An example of an exothermic reaction is provided by the combustion of a hydrocarbon:
The extensively measured enthalpy change for this reaction is,
Given the sign on
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?