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Chemical Reactions


Changes in matter ] Importance of chemical reactions ] [ Chemical Reactions ] On-line practice ]

A chemical reaction is a process in which substances called reactants are changed to produce new substances known as products.

Reactant A + Reactant B --> Product C + Product D

When chemical reactions take place between matter, new substances are formed.

Changes which take place in matter during chemical reactions are due to the arrangement of atoms and molecules.

No atoms are created or destroyed during chemical reactions, they simply rearrange themselves to form new substances.

A word equation is used to represent chemical reaction.

Examples :

Carbon + Oxygen --> Carbon dioxide

C + O2  --> CO2

A chemical reaction can only occur between particles when they collide (hit each other).
Particles may be atoms, ions or molecules.

There is a minimum amount of energy which colliding particles need in order to react with each other.
If the colliding particles have less than this minimum energy then they just bounce off each other and no reaction occurs.
This minimum energy is called the
activation energy.


The faster the particles are going, the more energy they have.
Fast moving particles are more likely to react when they collide.
You can make particles move more quickly by heating them up (raising the temperature).


Exothermic and endothermic changes ] Energy level diagrams ] Activation energy ] Rates of reaction ] Factors affecting rate of reaction ]