Question

Give one example each of which illustrates the following characteristics of a chemical reaction: (a) evolution of heat (b) change of colour (c) change in state​

Answer 1

Answer:

1.Evolution of gas:

The chemical reaction between zinc and dilute sulphuric acid is characterized by the evolution of hydrogen gas.

Zn(s)+H

2

SO4(aq)→ZnSO

4

(aq)+H

2

(g)

2.Change in colour:

The reaction between the lead nitrate solution and potassium iodide solution.

Pb(NO

3

)

2

(aq)+2KI→PbI

2

(s)+2KNO

3

(aq)

In this reaction colour changes from colourless to yellow.

3.Formation of precipitate:

The action of Barium Chloride on sodium sulphate.

BaCl

2

(aq)+Na

2

SO

4

(aq)→BaSO

4

(s)+2KNaCl(aq)

4.Change in temperature:

The action of dilute sulphuric acid on zinc:

Zn(s)+H

2

SO

4

(aq)→ZnSO

4

(s)+H

2

(g)

In this reaction, heat is evolved.

5.Change in the state:

When the wax is burnt in the form of the wax candle then water and carbon dioxide are formed. Wax is solid, water is a liquid whereas carbon dioxide is a gas.

Answer 2

a) When quick lime (Calcium oxide) reacts with water, calcium oxide is formed and heat evolved.

b) putting red food coloring and blue food coloring in a beaker of water results in purple water, but no chemical reaction has occurred.

c) a type of vaporization, occurs when particles of a liquid reach a high enough energy to leave the surface of the liquid and change into the gas state