How do we represent the heat evolved in exothermic reactions?
You might have to restate your question. I am unsure as to what you are asking.
We know that there are chemical reactions that release energy, for instance the combustion of hydrocarbons:
..or, very commonly.....
Now the energy that results from the formation of carbon dioxide and water can be measured (and of course be utilized to warm our baths and cook our breakfasts). By convention, this energy is reported as a NEGATIVE value.
Heat is written and included in product side to emphasize that the reaction is exothermic (release of heat).
Some, heat is considered product in an exothermic reaction, but this merely help to emphasize that heat is being released in the reaction. Always remember whether absorption/release of heat are just indicators that a chemical reaction has taken place and are quantifiable.