There isn't one specific equation that indicates an exothermic reaction. Instead, we use the enthalpy change (ΔH) in a chemical equation to determine if the reaction is exothermic or endothermic.

Here's how it works:

* Exothermic reaction: ΔH is negative. This means heat is released from the system to the surroundings.

* Endothermic reaction: ΔH is positive. This means heat is absorbed by the system from the surroundings.

Example:

Combustion of methane (exothermic):

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) ΔH = -890 kJ/mol

The negative ΔH indicates that 890 kJ of heat are released per mole of methane burned.

Important Note:

While ΔH is the most common indicator, you can also use other factors to determine if a reaction is exothermic, like:

* Temperature increase: If the temperature of the surroundings increases during the reaction, it's likely exothermic.

* Release of light or heat: Observing a flame or feeling heat generated during the reaction suggests exothermic behavior.

Remember, the key is to look for evidence of heat being released from the system, which is the defining characteristic of an exothermic reaction.