STD VIII – CHEMICAL REACTIONS (Online)

Introduction

This theme will enable children to understand that several oxides, carbonates and

hydrates on heating are converted to other compounds. Oxides of metals and non-metals have basic and acidic character respectively. They will also realize and appreciate that there are different types of reactions such as combinations, decomposition, displacement, double displacement, exothermic and endothermic reactions.

Burning a fuel is called combustion,

combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat. The original substance is called the fuel, and the source of oxygen is called the oxidizer. The fuel can be a solid, liquid, or gas.

 For combustion to occur three things must be present: a fuel to be burned, a source of oxygen, and a source of heat. As a result of combustion, exhausts are created and heat is released. We can control or stop the combustion process by controlling the amount of the fuel available, the amount of oxygen available, or the source of heat.

Types of Chemical Reactions

Combination or Synthesis reactions

Combination or Synthesis reactions

A combination or synthesis reaction is one, where a new product is synthesised by a combination of two or three reactants.

 ( X + Y → XY)

Decomposition reaction

Decomposition reaction is one, where one compound decomposes or breaks into two or more different products.

 (XY → X + Y).

Single Displacement reaction

When a cation or an anion is exchanged from a compound, this is called as single displacement reaction.

X + YZ → XZ + Y

Double displacement reaction

The anions are exchanged between two compounds or salts. Such reactions result in a different combination of cations and anions, at the end.

XY + AZ → XZ + AY

Oxidation

Addition of Oxygen atom, removal of a Hydrogen atom or loss of electrons.

Reduction

Addition of hydrogen atom, removal of oxygen, the gain of electrons.