Give four reasons why burning of a magnesium ribbon in air is considered a chemical change.

Compare the energy changes involved during a physical and a chemical change.

State which of the following terms connected with change of state of matter i.e.

(a) Melting

(b) Vaporisation

(c) Condensation

(d) Freezing

pertain to

(i) Conversion of a liquid into a vapour or gas.

(ii) Conversion of a liquid into a solid.

(iii) Conversion of a solid into a liquid on heating.

Potassium chloride is added to water and stirred. A salt solution is obtained which is then boiled leaving behind a residue

(a) Is the above change physical or chemical?

(b) Name the residue which remains behind after the salt solution is boiled.

(c) Is the change reversible or not reversible?

(d) Are the composition and properties of the original substance altered.

(e) Give a reason why the above experimentation would not be possible, if calcium carbonate is taken, in place of potassium chloride.