Changes in Matter: Physical and Chemical Changes - SS1 Chemistry Lesson Note

Changes in matter refer to the transformations that substances undergo, resulting in different properties or compositions. These changes can be classified into two main types: physical changes and chemical changes. Understanding the distinction between these types of changes is important in studying the behaviour and interactions of substances.

 

Physical Changes:

Physical changes are alterations in the physical state or appearance of a substance without changing its chemical composition. In a physical change, the molecules or atoms of the substance remain the same; only their arrangement or distribution changes. Some key characteristics of physical changes include:

 

1. Change in State: Physical changes often involve a change in the state of matter, such as solid to liquid (melting) or liquid to gas (vaporisation). For example, melting an ice cube to obtain liquid water is a physical change.
2. Reversible: Physical changes are usually reversible, meaning the original substance can be recovered by reversing the conditions. For instance, freezing water converts it back into ice.
3. No New Substances Formed: In physical changes, no new substances with different chemical properties are formed. The substance involved retains its identity throughout the change. An example of this is dissolving salt in water, where the salt particles disperse but do not chemically react.
4. Changes in Physical Properties: Physical changes may alter certain physical properties of a substance, such as shape, size, texture, or state. However, the fundamental chemical properties of the substance remain unchanged.

 

Chemical Changes:

Chemical changes, also known as chemical reactions, involve the formation of new substances with different chemical compositions and properties. In a chemical change, the atoms or molecules of the original substances rearrange, break bonds, and form new bonds to create new substances. Some key characteristics of chemical changes include:

 

1. Formation of New Substances: Chemical changes result in the formation of one or more new substances with distinct chemical properties. The original substances no longer exist in their original form. An example of a chemical change is the combustion of wood, where it reacts with oxygen to produce carbon dioxide and water.
2. Irreversible: Chemical changes are typically irreversible, meaning it is difficult or impossible to return to the original substances once the reaction has occurred.
3. Changes in Energy: Chemical changes are often accompanied by the release or absorption of energy in the form of heat, light, or sound. This energy change is an indication of the breaking and formation of chemical bonds during the reaction.
4. Changes in Chemical Properties: Chemical changes involve alterations in chemical properties, such as reactivity, flammability, or acidity. The new substances formed may have different chemical behaviours and properties compared to the original substances.