The process in which new substances with new properties are formed from one or more substances is called Chemical Reaction.
The substances which take part in chemical reaction are called Reactants.
The substances which are formed in a chemical reaction are called Products.
Examples :
(i) Digestion of food
(ii) Respiration
(iii) Rusting of iron
(iv) Burning of Magnesium ribbon
(v) Formation of curd
Chemical reaction involves :
• Change in state
• Change in colour
• Change in temperature
• Evolution of gas
Chemical Equation
A chemical reaction can be represented by chemical equation. It involves uses of symbol of elements or chemical formula of reactant and product with mention of physical state.
The necessary conditions such as temperature, pressure or any catalyst should be written on arrow between reactant and products.
e.g., Magnesium is burnt in air to form magnesium oxide.
2Mg + O2 → 2MgO
Balancing Chemical Equation
Law of conservation of Mass. Matter can neither be created nor destroyed in a chemical reaction.
So number of elements involved in chemical reaction should remain same at reactant and product side.