Physical ChangesPhysical changes begin and end with the same type of matter. Physical changes can be changes in size or shape, change in position or texture, and a change in state. The type of matter and properties do not change. Examples are an ice cube melting, cutting paper into different shapes or raking leaves. Water does not change its properties even if it is melted, frozen, or heated. Books and furniture cannot change state regardless of the amount of heat added to it.
Water can exist in more than one state. Water can exist as a solid, liquid, and gas. Taking away heat or losing heat causes matter to change from one state to another.
- For solids, when heat is added to it, the particles vibrate more rapidly, and cause the solid to change to a liquid.
- For liquids, adding more heat will cause the particles to move fast so that they break away from one another. Some particles may escape as gas.
- For gas, particles move fast and adding heat makes them move farther and faster apart. An example is pond water that evaporates faster in summer because of the higher air temperature which adds heat energy to the surface water. This causes the particles to move farther apart and escape as gas.
Chemical ChangesChemical changes are changes in matter. In a chemical change, matter has different properties from the one you started out with. A chemical change is also called a chemical reaction. Chemical changes involve taking in or giving off energy which maybe in the form of electricity, heat or light.
Some examples of chemical changes are the formation of table salt from sodium and chlorine. Also the formation of tarnish from a metal and oxygen. There are two products of a chemical change. The product is a compound or sometimes the product is the element making up a compound.
Chemical changes can be beneficial or harmful. Sugar is beneficial. Rust is harmful for a bridge especially when it can endanger cars and people from passing safely. To prevent some chemical changes, silver polish adds a protective layer to silver as it is cleaned.
There are some real-world chemical and physical changes. An example of a chemical change is toasted marshmallows. It occurs when oxygen combines with sugar, and carbon dioxide and water vapor is released. Another example of a chemical change is the browning of an apple. The oxygen in the air reacts with the exposed apple and results in browning. An example of a physical change is popcorn popping. The heat changes the popcorn kernel to gas and pressure builds up until the kernel pops.