Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer

• Change in temperature

When calcium oxide reacts vigorously with water to produce calcium hydroxide a large amount of heat is evolved and thus temperature of the system increases hence it confirms that a chemical reaction has been taken place.

• Gas evolution

When calcium carbonate is heated it decomposes into calcium oxide and carbon dioxide. Here carbon dioxide is a gas and thus confirms a chemical reaction