How is energy involved in physical and chemical changes?

Energy is involved in physical and chemical changes as it's either absorbed or released during these processes.

In physical changes, energy is involved in the form of heat, light or sound. For instance, when ice melts into water, it absorbs heat energy from the surroundings, making it an endothermic process. Conversely, when water freezes into ice, it releases heat energy to the surroundings, making it an exothermic process. Similarly, when a light bulb is switched on, electrical energy is converted into light and heat energy. These changes are physical because they do not alter the chemical composition of the substances involved.

Chemical changes, on the other hand, involve the breaking and forming of chemical bonds, which requires or releases energy. For example, in photosynthesis, plants absorb light energy to convert carbon dioxide and water into glucose and oxygen. This is an endotheric reaction as it absorbs energy. Conversely, in cellular respiration, glucose and oxygen are converted into carbon dioxide and water, releasing energy in the process. This is an exothermic reaction.

In both physical and chemical changes, the law of conservation of energy applies. This law states that energy cannot be created or destroyed, only transferred or transformed. Therefore, the total amount of energy before and after the change remains the same. For example, in a chemical reaction, the energy needed to break the bonds in the reactants is equal to the energy released when new bonds are formed in the products, plus or minus the energy absorbed or released as heat or light.

Understanding the role of energy in physical and chemical changes is crucial in chemistry. It helps us predict the outcomes of reactions, design energy-efficient processes, and understand natural phenomena.