- Chemical change is also called chemical reaction.
- Following are some signs of chemical reaction: Change in state, Change in colour, Evolution of gas, Change in temperature, etc.
- Chemical equation is a way of representing a chemical reaction in a simple way by using symbols for different factors of the reaction.
- A chemical equation can be written as word equation or by using symbols for different substances. Reactants are written on LHS of the arrow, while products are written on RHS of the arrow.
- When number of atoms of every element on LHS is same as that on RHS, the equation is called a balanced equation. In fact, a balanced equation obeys the law of conservation of mass.
- When a single product is formed from two or more reactants, then the chemical reaction is called combination reaction.
- When a substance gives two or more products after the chemical reaction, then the reaction is called decomposition reaction.
- When a salt solution of a less reactive metal reacts with a more reactive metal then the more reactive metal displaces the less reactive metal to form a new salt. This reaction is called displacement reaction.
- In some cases; when two salts react with each other then they displace each other to produce new salts. This reaction is called double displacement reaction.
- If a substance gains oxygen or loses hydrogen, then it is said to be oxidized.
- If a substance gains hydrogen or loses oxygen, then it is said to be reduced.
These main points are highly helpful for last minute preparation for examination. You can glance through them while going for examination. You can view them in the school bus, in car, in elevator, etc.