Which of the following is an irreversible reaction?

Options

A. `2NH_(3)rarrN_(2)+3H_(2)`
B. `PCl_(5)rarrPCl_(3)+Cl_(2)`
C. `KClO_(3)rarr KCl+O_(2)`
D. `SO_(3)rarrSO_(2)+O_(2)`

Answer

To determine which of the following reactions is irreversible, we need to analyze each option based on whether the reaction can proceed in both forward and backward directions.

1. **Option 1: 2NH3 ⇌ N2 + 3H2**
- This reaction can proceed in both directions. Ammonia (NH3) can decompose into nitrogen (N2) and hydrogen (H2), and nitrogen and hydrogen can react to form ammonia again. Therefore, this is a reversible reaction.

2. **Option 2: PCl5 ⇌ PCl3 + Cl2**
- Similar to the first option, this reaction can also proceed in both directions. Phosphorus pentachloride (PCl5) can decompose into phosphorus trichloride (PCl3) and chlorine gas (Cl2), and PCl3 and Cl2 can react to form PCl5 again. Thus, this is also a reversible reaction.

3. **Option 3: KClO3 → KCl + O2**
- This reaction involves the decomposition of potassium chlorate (KClO3) into potassium chloride (KCl) and oxygen gas (O2) upon heating. The products formed (KCl and O2) are stable and do not readily revert back to KClO3 under normal conditions. Therefore, this reaction is considered irreversible.

4. **Option 4: SO3 ⇌ SO2 + O2**
- This reaction can also proceed in both directions. Sulfur trioxide (SO3) can decompose into sulfur dioxide (SO2) and oxygen (O2), and SO2 can react with O2 to form SO3 again. Hence, this is a reversible reaction.

Based on the analysis above, the irreversible reaction among the options provided is:

**Answer: Option 3: KClO3 → KCl + O2**

---