EXERCISE

V. Answer the following questions in about four to five sentences.

1. What are the evidences of a chemical reaction?

Ans: The evidences of a chemical reaction are

          i. Production of gas.

         ii. Formation of precipitate.

        iii. Change in temperature.

         iv. Change in colour.

2. List the differences between physical and chemical changes.

Ans: physical changes: 

     i. Physical changes are mostly reversible.

     ii. No new substances are formed.

     iii. The substance(s) found retains its properties.

Chemical changes:

     i. All chemical changes are not reversible.

    ii. One or more new substances are formed.

    iii. the new substance is formed have different properties from the original substance.

3. Name the types of chemical reactions. Explain any one of them with a chemical equation.

Ans: The types of chemical reactions are given below: 

    i. Synthesis or combination reaction.

    ii. Decomposition reaction.

    iii. Single displacement reaction.

    iv. Double displacement reaction.

Synthesis or combination reaction: 


In this reaction hydrogen and oxygen combine to form one substance that is water. This type of chemical reaction where two or more substances combine to form one substance is called combination or synthesis reaction.

4. Explain crystallization.

Ans:- The process of forming crystals from pure substances which are solid at room temperature is called crystallization. By obtaining crystals, we are able to purify certain substances. Pure sugar, urea, copper sulphate, alum and table salt form crystals. Crystal of substances can be obtained from their saturated solutions.