Question

When is energy released during a chemical reaction?

Answer 1

In exothermic reactions, the products have less enthalpy than the reactants, and as a result, an exothermic reaction is said to have a negative enthalpy of reaction. This means that the energy required to break the bonds in the reactants is less than the energy released when new bonds form in the products.

Answer 2

The answer is: Exothermic reaction.

There are two types of reaction:  

1) Endothermic reaction (chemical reaction that absorbs more energy than it releases).

2) Exothermic reaction (chemical reaction that releases more energy than it absorbs).

For example, balanced chemical reaction:  

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O ΔrH= -1370 kJ/mol.  

This reaction is exothermic reaction (heat is released), so products have less potential energy and energy is transerred to surroundings.