For example: Chopping wood into pieces would be a physical change
Chemical reaction occurs due to the collision between the molecules of reactants which are in rapid motion in a chemical reaction. You'll know when an object has undergone a chemical change when the solution changes color, when a solid precipitates (a precipitation reaction), when the solution begins to bubble (which means that a gas is the product of the reaction), when the solution gives off heat (exothermic reaction),etc.
For example: Firework explosions
Precipitate, Exothermic and Endothermic
A precipitate process is basically double displacement reactions which involve the formation of solid residue that is called as a precipitate.
A precipitate process example would be Rain, snow, sleet, hail, fog, and other forms of water that comes from the sky.
An exothermic process releases heat, and causes the temperature of the immediate surroundings to rise.
An endothermic process absorbs heat and cools the surroundings. An example of an exothermic process is making ice cubes. An example of an endothermic process would be melting ice cubes.