Elements Compounds and Mixtures Part-3

Physical Change and Chemical Change

 Physical Property of a Substance:

Properties of a substance such as rigidity, colour, fluidity, boiling point, melting point, density and hardness which we can observe are called as Physical Properties.

 Physical Change:

When physical properties of a substance change it is known as a Physical Change. When we convert a substance from one state to another, such as a solid into a liquid or vice-versa, it is also a physical change as only the physical nature of the substance changes without affecting its chemical nature.

 

For Example, Change of ice into water. The chemical properties of water remain the same.

 Chemical Property of a Substance:

The chemical nature of a substance is known as its Chemical Property such as its odour or its chemical composition.

 Chemical Change:

When the chemical properties or chemical composition of a substance gets altered it is called a chemical change. It is also called as a Chemical Reaction.

For Example, Burning of paper

 Pure substances

Pure substances can be elements or compounds.

An element is a form of matter that cannot be broken down by chemical reactions into simpler substances.

A compound is a substance composed of two or more different types of elements, chemically combined in a fixed proportion.

 

Elements

Compounds

Cannot be broken into simpler substances.

Have fixed composition.

Can be broken down into elements by chemical or electrochemical reactions.

They have fixed melting and boiling point .

Example – Copper, oxygen, hydrogen etc

 

Example – water , NaCl , carbon dioxide .

 

Mixtures and compounds-

Mixtures

Compounds

1. Elements or compounds just mix together to form a mixture and no new compound is formed.

1. Elements react to form new compounds.

2. A mixture has a variable composition.

2. The composition of each new substance is always fixed.

3. A mixture shows the properties of the constituent substances.

3. The new substance has totally different properties.

4. The constituents can be separated fairly easily by physical methods.

4. The constituents can be separated only by chemical or electrochemical reactions.

Example – Air , sand and salt etc

Example – Water, carbon dioxide gas etc .