Endothermic reaction: A reaction in which reactants trap or absorb energy in the form of heat from its surroundings when forming products.
Exothermic reaction: A reaction in which the energy is released from the reacting system into surroundings.
Thermochemical equation: Is a balanced chemical equation that includes the enthalpy change (ΔH) associated with the reaction. It represents the reactants and products involved in a chemical reaction along with the amount of heat energy exchanged during the reaction.
Enthalpy Change (ΔH): is a state function that represents the amount of heat energy that is absorbed or released during a chemical reaction.
There are several ways to determine if a reaction is endothermic or exothermic given a enthalpy value:
1. If the value is given in a question where it is not associated within the chemical equation then we must look at the sign of the enthalpy value.
- if ΔH is negative, then it is an exothermic reaction
- if ΔH is positive, then it is an endothermic reaction
2. If the enthalpy value is embedded as a reactant or product, we must look at what side the value is on.
- if ΔH is on the reactant side. then it is an endothermic reaction
- if ΔH is on the product side, then it is an exothermic reaction
Given the heat term on the reactant side it indicates an endothermic reaction.