Reaction with acid/base
Reaction with water
Physical changes occur when the substance involved remains that same substance (i.e. candle wax vaporized or melting – it is still candle wax). Changes of state are physical changes as well as dissolving. Most physical changes are easy to reverse.
In a chemical change the original substance is changed into one or more different substances. Most chemical changes are difficult to reverse. (i.e. burning, cooking, and rusting).
Clues that a chemical change has occurred include:
· New colour appears
· Heat or light given off
· Bubbles of gas formed
· Precipitate forms in a liquid
· The change is difficult to reverse
Chemical or physical change? Why?
1. garbage rotting
2. cutting up carrots
3. silver spoon turning black
4. making tea from tea leaves
5. bleaching a stain
6. boiling an egg
Matter can be broken down into 2 categories.
1. Pure substances contain only 1 type of particle and therefore the substance has constant properties (i.e. water freezing at 0oc). Pure substances can be broken down into 2 more categories (elements and compounds). Elements are identified by chemical symbol (C). Compounds are pure substances that contain 2 or more different elements (H2O).
2. A mixture contains at least 2 different pure substances or 2 different types of particles. A solution may be made up of liquids, solids or gases. Air is a solution of gases, perfumes are solutions of alcohols. A heterogeneous mixture is a substance in which the different components are identifiable and can be separated by physical means (i.e. pizza).