Definitions [14]
Define a chemical change. Give two examples of the above changes.
A permanent change in which new substances are formed whose composition and properties are completely different from those of the original
substances.
Chemical change:
(i) Burning of wood.
(ii) Breathing.
Define physical change. Give two examples for the above changes.
Physical change: A temporary change in which no new substance is formed, the composition of substance remains the same, though its state, shape and size may change.
Example of physical change:
- Change of water into its vapours.
- Heating of iron rod.
Define electrolysis.
The cell which converts electrical energy into chemical energy is called an electrolytic cell and the process which converts electrical energy into chemical energy is called electrolysis.
Define a photochemical reaction.
A chemical reaction that occurs in the presence of light is called a photochemical reaction.
Define catalyst.
A catalyst is a substance that either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change during the reaction.
Define chemical reaction.
Any chemical change in matter that involves its transformation into one or more new substances is called a chemical reaction.
Define an electrochemical reaction.
An electrochemical reaction is a chemical reaction involving the transfer of electrons, where oxidation and reduction occur simultaneously.
Define the following term:
Precipitate
Chemical reactions which are characterised by the formation of insoluble solid substances are called precipitates.
Define precipitation reaction.
A chemical reaction in which two compounds in their aqueous state react to form an insoluble salt as one of the products.
Define the following term:
Chemical change
A chemical change is a permanent change in which the chemical composition of a substance is changed and one or more new substances with different chemical compositions and different properties are formed.
The substances formed as a result of a chemical reaction by formation of new bonds are called products.
A chemical change is a process in which the composition of matter changes, resulting in the formation of one or more new substances.
The substances taking part in chemical reaction are called reactants.
Corrosion is the gradual damage of metals caused by their reaction with components of the atmosphere, such as oxygen and moisture.
