Question

(a) State the various characteristics of chemical reactions.

(b) State one characteristic each of the chemical reaction which takes place when :
(i) dilute hydrochloric acid is added to sodium carbonate

(ii) lemon juice is added gradually to potassium permanganate solution

(iii) dilute sulphuric acid is added to barium chlorid solution

(iv) quicklime is treated with water

(v) wax is burned in the form of a candle

Answer 1

Following are the various characteristics of a chemical reaction:

1. Evolution of gas: Zinc and dilute sulphuric acid react to form zinc sulphate with the evolution of hydrogen gas.
2. Formation of precipitate: Sulphuric acid and barium chloride react to form white precipitates of barium sulphate.
3. Change in colour: Purple colour of potassium permanganate solution on addition of citric acid changes to colourless solution.
4. Change in temperature: Barium hydroxide and ammonium chloride react to form barium chloride, ammonia and water. This is an endothermic reaction in which heat is absorbed, causing the temperature to fall.
5. Change in state: Combustion of candle wax (solid) leads to the formation of water (liquid) and carbon dioxide (gas).

1. (b)
   (i) When sodium carbonate is added to dilute hydrochloric acid, carbon dioxide gas evolves. Hence, this reaction is characterised by evolution of gas.
   
   (ii) Lemon juice (contains citric acid) changes the purple colour of potassium permanganate solution to a colourless solution. Hence, this reaction is characterised by change in colour.
   
   (iii) When dilute sulphuric acid is added to barium chloride solution, it forms white precipitates of barium sulphate. Hence, this reaction is characterised by formation of precipitate.
   
   (iv) When quicklime is treated with water, slaked lime is formed with the evolution of large amount of heat. Hence, this reaction is characterised by change in temperature.
   
   (v) When wax (solid) is burnt in the form of candle, it produces water (liquid) and carbon dioxide (gas). Hence, this reaction is characterised by change in state.