State what is a chemical reaction. A chemical reaction is often accompanied by external indications or characteristics which include

(a) Colour change

(b) Effervescence or gas evolved

(c) Evolution or absorption of heat

(d) Formation of a precipitate

With reference to each of the above indications, state the external indication seen during

(i) Addition of dilute acid to an active metal

(ii) Addition of dilute hydrochloric acid to silver nitrate

(iii) Addition of water to quicklime

(iv) Thermal decomposition of mercury [II] oxide

Differentiate between Direct combination reaction & a decomposition reaction.

Differentiate between Displacement reaction & a neutralization reaction.

Classify the following reactions into

(a) Direct combination

(b) Decomposition

(c) Displacement

(d) Double decomposition

The reactions are

(i) Zinc hydroxide on heating gives zinc oxide & water

(ii) Zinc reacts with copper [II] sulphate to give zinc sulphate & copper

(iii) Zinc sulphate reacts with ammonium hydroxide to give ammonium sulphate & zinc hydroxide

(iv) Molten zinc at high temperatures, burns in air to give zinc oxide.