i. Give an example for a combination reaction which is exothermic. ii. Identify the oxidising agent, reducing agent in the following reaction: H 2 S + Cl 2 ⇒ 2HCl + S iii. Name the phenomenon due to which the taste and smell of oily food changes when kept for a long time in open. Suggest one method to prevent it.

Question

Philoid · Accepted Answer

(i) Combination reactions are those reaction in which two compounds combine to give one product. Combination reactions are always exothermic.

CaO + H₂O → Ca(OH)₂ + Heat

(ii) An oxidising agent is one which oxidises to something and a reducing agent is one which reduces to something.

In this reaction, H₂S is a reducing agent because it is reducing to Cl₂ and Cl₂ is an oxidising agent because it is oxidising to H₂S.

(iii) The phenomenon due to which the taste and smell of oily food changes when kept for a long time in open is known as rancidity. It is prevent by keeping the oily food in airtight container.