Exothermic and Endothermic Reactions

• Exothermic and Endothermic reactions are two types of energy changes that can occur in chemical reactions.

• Exothermic reactions release energy, usually in the form of heat, light, sound, or electricity. In an exothermic reaction, the energy of the products is less than the energy of the reactants.

• Common examples of exothermic reactions include combustion, such as a fire, and neutralisation reactions, such as mixing acid and base.

• The symbol for energy in chemical equations is usually E or ΔH. A negative ΔH (-ΔH) represents an exothermic reaction because energy is lost from the system to the surroundings.

• Endothermic reactions absorb energy from the surrounding environment. This absorption of energy can be felt as a decrease in temperature.

• In an endothermic reaction, the energy of the products is greater than the energy of the reactants. Examples of endothermic reactions include photosynthesis and the process of ice melting.

• An endothermic reaction is signified by a positive ΔH (+ΔH) in chemical equations because energy is gained from the surroundings into the system.

• Energy diagrams can be useful tools to visualise the energy changes in exothermic and endothermic reactions.

• In an energy diagram, the difference between the energy level of the reactants and the products gives the energy change for the reaction. In an exothermic energy diagram, the energy level of the products is lower than the reactants, and in an endothermic energy diagram, the energy level of the products is higher than the reactants.

• The understanding of exothermic and endothermic reactions is vital for various fields like industrial processes, environmental science, and even cooking. Knowing how certain chemicals react under specific conditions allows us to control and utilise their energy changes for various uses.

• Experiments, such as the heating or cooling of certain chemicals in a laboratory, can be carried out to determine whether a reaction is exothermic or endothermic.

• It is important to note the role of activation energy in these reactions. The activation energy is the minimum amount of energy required for a reaction to occur. It can be thought of as the energy needed to start the reaction.

• Catalysts can be used to lower the activation energy in both exothermic and endothermic reactions, hence making the reaction occur faster.