Question

State the various characteristics of chemical reactions.

Answer 1

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: The purple colour of the potassium permanganate solution, upon the addition of citric acid, changes to a 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).