Question

State what is a chemical reaction. A chemical reaction is often accompanied by external indications or characteristics which includes 1.colour change 2.effervesence or gas evolved 3. Evolution or absorption of heat 4. Formation of precipitate. With reference to each of the above indications, State the external indications seen during - 1. Addition of dilute acid to an active metal 2. Addition of dilute hydrochloric acid to silver nitrate. 3. Addition of water to quicklime. 4. Thermal decomposition of mercury(ll) oxide

Answer 1

Chemical reaction : Is a chemical change in which matter changes into a new substance or substances

1.. Addition of dilute acid to an active metal - gas is evolved, test tube or flask becomes hot.

2.Addition of dilute hydrochloric acid to silver nitrate. - a white coloured precipitate of Agcl is seen.

3.Addition of water to quicklime. - hissing sound accompanied by a lot of heat ( boiling)

4. Thermal decomposition of mercury(ll) oxide - red colour of H[II]0 changes to silver (Hg metal).