$(a)$ Study the following chemical equation:
$CaSO_4 \cdot 2H_2O \xrightarrow{373K} CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O$
Name the reactant and the product. State one use of the product.

(N/A) Reactant: $CaSO_4 \cdot 2H_2O$ is known as Gypsum.
Product: $CaSO_4 \cdot \frac{1}{2}H_2O$ is known as Plaster of Paris $(POP)$.
Use: It is widely used by doctors as plaster for supporting fractured bones in the right position or for making toys,materials for decoration,and surfaces for smooth finishing.