10th Class Science Chemical Reactions and Equations

 Chemical Reactions and Equations

• Chemical reactions

A chemical reaction is a process in which substances undergo change to produce new substances with new properties. The substances which take part in a chemical reaction are known as reactants. The new substances formed during a chemical reaction are known as products.

• The important characteristics of chemical reactions are: evolution of a gas, formation of a precipitate, change in colour, change in temperature, and change in state.

• Chemical equations

A chemical equation is a short hand representation of a chemical reaction using symbols and formulae of the substances involved in the reaction.

• A balanced chemical equation is the one which contains equal number of atoms of each element on both sides of the equation.

• Types of chemical reactions

The reaction in which two or more substances combine to produce a single substance is known as synthesis reaction or combination reaction.

• The reaction in which a compound is broken down into two or more simpler substances is known as decomposition reaction.

• A reaction in which an atom or a group of atoms present in a molecule is displaced by another atom is known as displacement reaction.

• A reaction in which two compounds exchange their ions to form two new compounds is known as double displacement reaction.

• Double displacement reactions are also called double decomposition reactions or metathesis reactions.

• Reactions in which heat is given out along with the products are called exothermic reactions.

• Reactions in which heat is absorbed by reactants to form products are called endothermic reactions.

• Oxidation and reduction reactions

Oxidation is defined as the addition of oxygen or removal of hydrogen to a substance.

• Oxidation is also defined in terms of metals and non-metals as the addition of non-metallic element (or removal of metallic element).

• Reduction is addition of hydrogen or removal of oxygen to a substance.

• Reduction is also defined in terms of metals and non-metals as the addition of metallic element (or removal of non-metallic element).

• The substance which oxidizes substances is known as an oxidizing agent.

• The substance which reduces substances is known as a reducing agent.

• In redox reactions, oxidation and reduction reactions occur simultaneously.