chemistry is the branch of science that deals with the composition, properties and uses of matter.

It investigates into the changes that matter undergo.

  matter is anything that have mass or occupy space. It is built up of elementary particles such as element , ions and molecules.

Mass is the quantity of matter a substance contains. For practical purposes, it is measured in grams(g).

There are 3 states of matter. They are;

1. solid state

2. liquid state

3.Gases state

The solid has a definite shape and definite volume.The liquid has no definite shape but have a definite volume.The gas has neither definite shape or volume.These states can change from one form to  another. Solid to liquid e.g ice block to water. Solid to gas which is known as sublimation. Example of such solid is Ammonium chloride.Liquid to solid e.g water to ice. Liquid to gas e.g water to vapor.Gas to liquid which is known as condensation e.g vapor to water.

  There are two basic changes that matter undergoes: physical and chemical changes.

Physical changes are those changes that are reversible and in which no new substances are formed.e.g change from water to ice which can be reversed .

Chemical changes are those changes that are not reversible and in which new substances are formed. e.g the burning of wood to form ash.

 The major difference between the two changes is that the physical change is reversible while the chemical change is irreversible.  Also, no new substance is formed in physical change but new substances are formed in chemical change.