How can you tell if a reaction is exothermic from its equation?

A reaction is exothermic if its equation shows heat being released, often represented as ΔH being negative.

In a chemical equation, an exothermic reaction is typically indicated by the presence of heat on the product side of the equation. This is because in an exothermic reaction, heat is released as a product. For example, in the combustion of methane (CH4 + 2O2 → CO2 + 2H2O), heat is released, making it an exothermic reaction. However, this heat is not always explicitly written in the equation.

Another way to identify an exothermic reaction from its equation is by looking at the enthalpy change, represented as ΔH. The enthalpy change is the difference in the total amount of energy in the reactants and the products. If the enthalpy change is negative (ΔH < 0), it means that the total energy of the products is less than the total energy of the reactants. This indicates that energy has been released during the reaction, making it an exothermic reaction.

In summary, an exothermic reaction can be identified from its equation by looking for heat as a product or a negative enthalpy change. However, it's important to remember that not all equations will explicitly show these indicators. In such cases, you may need to refer to other sources of information, such as enthalpy change tables or your knowledge of common exothermic reactions, to determine whether a reaction is exothermic.