Chemical Reaction

Many changes take place in our surroundings everyday.

Cooking of food, burning of fuel are the reactions in which substances are totally transformed. Such transformations are called chemical changes.

The event in which substance gets transformed

permanently (Chemical changes) is called chemical reaction.

The things we use daily are formed because of

chemical reactions. e.g : The painted walls , things made from plastics

To represent chemical reaction they are written in the form of equation

e.g When Calcium Oxide reacts with water, it produces a single compound, Calcium hydroxide and energy is

released. • This reaction is represented in equation form as under.• CaO + H2O Ca(OH)2 + energy Calcium Oxide Water Calcium Hydroxide

CaO + H2O Ca(OH)2

• In a chemical reaction, reactants are written on left hand side of the arrow whereas products are written on right hand side of arrow.

• The substances taking part in a chemical reaction are called reactants and the substances formed during the reaction are called products.

Types of Chemical reactions

• Combination reactions• Reactants two or more than two• Product only one

• e.g : C + O2 CO2

Decomposition reaction

• Reactant only one,• Products more than one• e.g : 2H2 0 2H2 + O2

Displacement Reaction

• Two or more reactants and products

• One constituent from the reactant displaces another constituent and separates it to form

the product.

• e.g : Zn + 2HCl ZnCl2 + H2

Oxidation and reduction

• Oxidation- Oxygen combines with an element

or a compound. e.g : C + O2 CO2 • Reduction - A reaction in which hydrogen

combines with an element or compound or a reaction in which oxygen is lost from a compound

Cl2 + H2 2HCl

The speed of chemical reactions

Some chemical reactions are fast whereas some

reactions takes place slowly. e.g : Ripening of fruits, rusting of iron(Slow), Burning of Paper, Lightening of fire crackers(Fast)

Various factors such as the size of the reactant particles, their temperature and concentration and the presence of catalysts affect the speed of reaction.

Catalyst doesn’t take part in chemical reaction, it’s mere presence speeds up a chemical

reaction.e.g: Manganese dioxide, Raney nickel

In some chemical reactions, heat is given out. (Exothermic Reaction)

e.g : Burning of Magnesium in air.

In some chemical reactions heat is absorbed.(Endothermic reactions)

e.g: dissolving of urea in water

ADD EXPERIMENT

Following changes are observed during a chemical reaction

-Change in the state of the substance

- Change in temperature

- Change in colour

- Generation of gas