Chemical Reaction The transformation of a chemical substance into another chemical substance. Common observations– Change in state, colour and temperature Evolution of gas Formation of precipitate

Chemical Equation Representation of chemical reaction using symbols of substances to represent in a concise and informative way. For convenience, symbol of substance is used.

Reactant: Substances which take part in a chemical reaction. Product: New substance formed after a chemical reaction. A+B→C+D A & B are reactants and C & D are products

Balanced Chemical Equation– If number of atoms of each element equal on both sides. Unbalanced Chemical Equation– If the no. of atoms of each element in reactants and products are not equal.

Making Chemical Equation More Informative– • By writing symbols of the physical states of substances • By writing the condition in which reaction takes place

Exothermic Reaction– Reactions which produce energy. Eg- Respiration Endothermic Reaction– Reactions which absorb/require energy. Eg- Photosynthesis

Types of Chemical Reaction – a. Combination Reactions– Reactions in which two or more reactants combine to form one product. Ex- 2Mg + O2 → 2MgO

b. Decomposition Reactions– Reactions in which 1 compound decomposes in 2 or more compounds or element. Ex- CaCO3→CaO+CO2 Its types are: Thermal Decomposition- It uses energy in the form of heat

Electrolysis- It uses electricity for the decomposition of the reactant molecules. Ex- 2H2O → 2H2 + O2 Photolysis- It uses light energy for decomposition. Ex- 2AgCl → 2Ag + Cl2

c. Displacement Reaction – Reactions in which atoms or ions move from one compound to other to form new compound. It takes place only when ‘A’ is more reactive than B. A + BC → AC + B

d. Double Displacement Reaction– Reactions in which ions are exchanged between two reactants forming new compounds. Ex- Neutralisation reactions AB + CD → AD + CB

Oxidation– process of gaining oxygen or losing hydrogen during a reaction. Reduction– process of losing oxygen or gaining hydrogen during a reaction.

Redox Reactions: The reaction in which oxidation and reduction take place simultaneously. In REDOX, ‘Red’ stands for reduction and ‘Ox’ stands for oxidation. Eg- CuO + H2 → Cu + H2O