Q1. [1] medium thorough-understanding
Which of the following correctly pairs a reaction type with its energy relationship?
(A) Decomposition of water by electricity — exothermic; combination of CaO with water — endothermic
(B) Decomposition of water by electricity — endothermic; combination of CaO with water — exothermic
(C) Both reactions are exothermic
(D) Both reactions are endothermic
- A Decomposition of water by electricity — exothermic; combination of CaO with water — endothermic
- B Decomposition of water by electricity — endothermic; combination of CaO with water — exothermic
- C Both reactions are exothermic
- D Both reactions are endothermic
Generated by claude-sonnet-4-6 · 2026-06-26 00:55 · grounding rag
Model Answer
(B) Decomposition of water by electricity — endothermic; combination of CaO with water — exothermic.
Explanation
Electrolysis of water requires electrical energy to be absorbed, making it endothermic. The reaction of CaO with water releases a large amount of heat, making it exothermic. The textbook explicitly states CaO + H₂O → Ca(OH)₂ + Heat.