3.1 Chemical and Physical Changes
1 Identify physical and chemical changes, and understand the differences between them.
Chemical Changes: These occur when a substance combines with another to form a new substance
- Rotting fruit
- Mixing chemicals
- Tarnishing silver.
Physical changes: These are changes that affect the form of an object, but ultimately doesn’t have any effect on its chemical composition.
- Tearing a piece of tin foil.
- Crumpling a piece of paper.
Differences between the two:
1. A physical change is reversible, a chemical change is not. For example, the freezing of water would be a physical change because it can be reversed, whereas the burning of wood is a chemical change – you can’t ‘unburn’ it
2. A physical change is a change in which no new substance is formed; a chemical change results in the formation of one or more new substances. Again, consider the previous examples: Freezing water into ice just results in water molecules which are ‘stuck’ together – it’s still H2O. Whereas burning wood results in ash, carbon dioxide, etc, all new substances which weren’t there when you started.
You’re messing around with the physical structure object, but that’s it.