**Heating Gypsum to Form 'X' Compound**

**a) Chemical Equations of the Reactions:**
When gypsum (calcium sulfate dihydrate, CaSO4·2H2O) is heated at 373K (100°C), it undergoes a dehydration reaction to form a new compound, 'X'. The chemical equation for this reaction can be represented as:

CaSO4·2H2O (gypsum) → CaSO4·½H2O + 1½H2O

**b) Chemical Name and Uses of 'X' Compound:**
The compound 'X' formed during the dehydration of gypsum is calcium sulfate hemihydrate, also known as plaster of Paris (CaSO4·½H2O). Some of the uses of plaster of Paris are:

1. Construction and Building Materials: Plaster of Paris is widely used in the construction industry for various purposes, including creating decorative elements, making plasterboards, and forming molds for casting concrete or other materials.

2. Medical and Dental Applications: Plaster of Paris is used in medical and dental fields for making casts and molds. It is commonly used to immobilize broken bones by creating casts that provide support and protection during the healing process.

**c) Reaction between 'X' Compound and Gypsum:**
The reaction between the 'X' compound (calcium sulfate hemihydrate) and gypsum (calcium sulfate dihydrate) involves the rehydration of 'X' to form gypsum again. The reaction equation can be represented as:

CaSO4·½H2O + 1½H2O → CaSO4·2H2O

Explanation:
- The reaction between the 'X' compound and gypsum is a reverse of the dehydration process.
- When the 'X' compound is exposed to water (1½H2O), it absorbs the water molecules and converts back into gypsum (CaSO4·2H2O).
- This reaction is often utilized in the setting and hardening of plaster of Paris. When plaster of Paris is mixed with water, it undergoes rehydration and sets into a solid form, allowing it to be used for various applications, such as casting molds or creating solid structures.
- The rehydration process is exothermic, releasing heat as the gypsum crystals reform and solidify.

Overall, the heating of gypsum at 373K leads to the dehydration of gypsum, forming the 'X' compound (calcium sulfate hemihydrate or plaster of Paris). This compound has various applications in construction, medicine, and dentistry. When the 'X' compound is mixed with water, it undergoes rehydration and transforms back into gypsum, allowing it to be used for casting and molding purposes.

When gypsum is heated at 373 k POP is formed the reaction can be represented as-CasO4 .2H2O heat(373K)= CasO4.1/2H2O+1 1/2 H2O So here the compound X is POP ( calcium sulphate hemihydrate)