Types of Chemical Reactions Chemical reactions involve the breaking and forming of chemical bonds, resulting in the rearrangement of atoms to create new substan...
Chemical reactions involve the breaking and forming of chemical bonds, resulting in the rearrangement of atoms to create new substances with different properties. There are two main types of reactions classified based on the energy changes involved:
Exothermic reactions release energy to the surroundings, resulting in an increase in temperature. Examples include combustion reactions like burning wood or fossil fuels. The reaction profile shows a lower energy level for the products compared to the reactants.
Endothermic reactions absorb energy from the surroundings, causing a decrease in temperature. Examples include photosynthesis and the thermal decomposition of calcium carbonate. The reaction profile shows a higher energy level for the products compared to the reactants.
A reaction profile graphically represents the energy changes during a chemical reaction. It shows the activation energy barrier that must be overcome for the reaction to proceed. The activation energy is the minimum energy required to initiate a chemical reaction by breaking bonds in the reactants.
In this exothermic reaction, the products have a lower energy level than the reactants, releasing excess energy as heat.
During a chemical reaction, bonds in the reactants must be broken, which requires an energy input. Simultaneously, new bonds are formed in the products, releasing energy. The overall energy change depends on the difference between the energy required for bond breaking and the energy released during bond formation.
Chemical reactions can be harnessed to generate electricity in devices like chemical cells and fuel cells.
Chemical cells convert the energy from spontaneous redox (reduction-oxidation) reactions into electrical energy. A common example is the dry cell battery, where the redox reaction between zinc and an electrolyte generates an electrical current.
Fuel cells are devices that convert the chemical energy from a fuel (e.g., hydrogen) into electrical energy through an electrochemical reaction with oxygen. They are more efficient and environmentally friendly than combustion-based energy sources.
For more information, refer to the BBC Bitesize guide on chemical reactions and your exam board's official specification.