Question

Calcium oxide reacts vigorously with water to produce slaked lime. $\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)\to \mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)$ This reaction can be classified as:

• A. Combination reaction.
• B. Exothermic reaction.
• C. Endothermic reaction
• D. Oxidation reaction.

Answer 1

Answer: (A), (B)

Exothermic reaction.

Combination reaction: Combination reactions are those reactions in which two or more elements are combined together to form a single product.

Exothermic reaction: Exothermic reactions are those reactions in which heat energy is evolved.

Endothermic reaction: Endothermic reactions are those reactions in which heat energy is given to proceed with the reaction.

Oxidation reaction: Oxidation reactions are those reactions in which oxygen is added or hydrogen is removed from the reactant.

The explanation for correct options.

In the given reaction.

$$\begin{gathered} \mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)\to \mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right) \\ \mathrm{Calcium}\mathrm{water}\mathrm{Calcium} \\ \mathrm{Oxide}\mathrm{hydroxide} \end{gathered}$$

Part A) Lime or Calcium oxide (CaO) combines with water to form slaked lime Ca(OH)₂(aq). Hence, two substances are combined to form a single substance, therefore it is a combination reaction.

Part B) When lime is treated with water, a lot of energy is evolved, therefore it is an exothermic reaction.

The explanation for incorrect options.

1. Since no heat energy is given two complete the reaction, hence it cannot be an endothermic reaction, therefore option (C) is wrong.
2. no addition of oxygen or removal of hydrogen occurs in the reaction, therefore it cannot be an oxidation reaction, therefore option (D) is wrong.

Hence, option A) and B) are correct.