STD-X       CHEMICAL REACTIONS AND EQUATIONS          CAPSULE -1        07-04-2016

Chemical reactions and equations for std-X

Chemical reactions are the processes in which new substances with new properties are formed.

• Only a rearrangement of atoms takes place in a chemical reaction.
• The substances which take part in a chemical reaction are called reactants.
• The new substances produced as a result of chemical reaction are called products.
• In a chemical reaction, reactants are transformed into products.
• The burning of magnesium in air to form magnesium oxide is an example of a chemical reaction.

Characteristics of Chemical reactions

• The conversion of reactants into products in a chemical reaction is often accompanied by some features which can be easily observed easily.
• The important characteristics of chemical reactions are:
1. Evolution of a gas
2. Formation of a precipitate
3. Change in colour
4. Change in temperature
5. Change in state

 

Chemical equations:

• The method of representing a chemical reaction with the help of symbols and formulae of the substances involved in it is known as a chemical equation.

Zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas.
Zinc   +   Sulphuric acid  =  Zinc Sulphate   + Hydrogen
Zn   +     H2SO4    ZnSO4  +  H2

• The substances which combine or react are known as reactants.
• The new substances produced in a reaction are known as products.
• A chemical equation is a short-hand method of representing a chemical reaction.

 

Types of chemical reactions

Some of the important types of chemical reactions are:

1. Combination reactions
2. Decomposition reaction
3. Displacement reactions
4. Double displacement reactions 
5. Oxidation and Reduction reactions

Combination reactions:

Those reactions, in which two or more substances combine to form a single substance, are called combination reactions.

• In a combination reaction, two or more elements can combine to form a compound; two or more compounds can combine to form a new compound; or an element and a compound can combine to form a new compound.