Question

When dry chlorine gas is passed over molten white phosphorus, a mixture of wo chlorides (phosphorus trichloride and phosphorus pentachloride) is obtained. The hosphorus gives phosphorus trichloride with limited supply of chlorine and hosphorus pentachloride with excess chlorine …?

Answer 1

When dry chlorine gas is passed over molten white phosphorus (P₄), different reactions take place depending on the amount of chlorine available:

1. **Limited Supply of Chlorine**:
- When there is a limited supply of chlorine gas, phosphorus primarily reacts to form **phosphorus trichloride (PCl₃)**. The reaction can be represented as follows:
\[
P_4 + 6Cl_2 \rightarrow 4PCl_3
\]
- This reaction occurs due to the availability of chlorine being insufficient to convert all phosphorus into phosphorus pentachloride.

2. **Excess Supply of Chlorine**:
- When chlorine is supplied in excess, phosphorus can be fully chlorinated to form **phosphorus pentachloride (PCl₅)**. The reaction in this case can be represented as:
\[
P_4 + 10Cl_2 \rightarrow 4PCl_5
\]
- Here, the excess chlorine allows all the phosphorus to react completely, resulting in the formation of phosphorus pentachloride.

**Summary**: The products depend on the amount of chlorine gas available:
- Limited chlorine → Phosphorus trichloride (PCl₃)
- Excess chlorine → Phosphorus pentachloride (PCl₅)