Chemical Reactions and Equations

Valency can be termed as the combining capacity of an atom , ie the number of electrons it can gain , loose or share

Observations in a reaction

  1. Change in state

  2. Change in colour

  3. Change in temperature

  4. Formation of precipitate

  5. Evolution of gases

Chemical Equations vs Chemical Reaction

Balancing of Chemical Equations

LOCM

Matter can neither be created nor destroyed in a chemical reaction , ie: the sum of the masses of the reactants must be equal to the sum of the masses of the product.

We balance chemical equations so that the law of conservation of mass is followed.

Types of Chemical Reactions

1.Combination Reaction

The reaction in which two or more substances combine to form a new substance. Examples - burning of magnesium ribbons. They are generally exothermic

2. Decomposition Reactions

Decomposition Reactions are generally endothermic in nature.

A. Thermal Decomposition

Examples - Heating calcium carbonate , Iron Sulphide , Lead Nitrate

B. Electrolytic Decomposition

Example - electrolysis of water

C. Photolytic Decomposition

Examples - silver chloride , silver bromide