Define exothermic and endothermic reactions and... - SS1 Chemistry Energy Changes in Chemical Reactions Question

Exothermic and endothermic reactions are two types of chemical reactions that differ in terms of energy transfer and the direction of heat flow.

 

1. Exothermic reactions: Exothermic reactions release energy in the form of heat to the surroundings. In these reactions, the energy of the products is lower than the energy of the reactants, resulting in a net release of energy. The heat flow is from the system (reactants) to the surroundings. Examples of exothermic reactions include:

-       Combustion reactions: When a substance reacts with oxygen to produce carbon dioxide and water, such as the combustion of gasoline or the burning of wood.

-       Neutralisation reactions: The reaction between an acid and a base to form water and a salt, such as the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) to produce water (H2O) and sodium chloride (NaCl).

-       Some oxidation reactions: For example, the reaction between iron (Fe) and oxygen (O2) to form iron(III) oxide (Fe2O3) in the process of rusting.

 

1. Endothermic reactions: Endothermic reactions absorb energy from the surroundings. In these reactions, the energy of the products is higher than the energy of the reactants, resulting in a net absorption of energy. The heat flow is from the surroundings to the system. Examples of endothermic reactions include:

-       Dissolving certain salts in water: For example, the dissolution of ammonium nitrate (NH4NO3) in water.

-       Photosynthesis: The process by which plants convert carbon dioxide (CO2) and water (H2O) into glucose and oxygen (O2) using energy from sunlight.

-       Some decomposition reactions: For example, the thermal decomposition of calcium carbonate (CaCO3) to form calcium oxide (CaO) and carbon dioxide (CO2) requires an input of heat.