Question

Is the reaction between quick lime and water endothermic or exothermic?

Answer 1

Endothermic reaction:

• A reaction that the system absorbs energy from its surrounding in the form of heat.

Exothermic reaction:

• A reaction that releases energy from the system in the form of heat.

The reaction between quick lime and water:

• Quick lime is chemically known as Calcium oxide $\left(\mathrm{CaO}\right)$ which is made up of Calcium and Oxygen atoms.
• When Calcium oxide $\left(\mathrm{CaO}\right)$ reacts with water, Calcium hydroxide$\left(\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\right)$ is formed.

$\underset{\mathrm{Calcium}\mathrm{oxide}}{\mathrm{CaO}\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Calcium}\mathrm{hydroxide}}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Heat}}{∆}$

• When the reaction occurs a huge amount of energy is released, so this is an exothermic reaction.
• The reaction of the formation of Calcium hydroxide from Calcium oxide and water is a combination reaction because there is only one product is formed from the two reactants.

Therefore, the reaction between quick lime and water is exothermic.