Which of the following is not a physical equilibrium?

Options

A. `ice iff water`
B. `I_2(s) iff I_2(g)`
C. `S(l) iff S(g)`
D. `3O_2 iff 2O_3`

Answer

To determine which of the following options is not a physical equilibrium, we first need to understand what physical equilibrium is. Physical equilibrium occurs when a substance undergoes a change from one physical state (or phase) to another, such as solid to liquid or liquid to gas, without altering its chemical composition.

### Step-by-Step Solution:

1. **Understand Physical Equilibrium**:
- Physical equilibrium refers to the state where a physical process, such as phase changes, occurs without any change in the chemical identity of the substance.

2. **Identify the Options**:
- We need to analyze each option provided to see if they represent a physical change or not.

3. **Analyze Option 1**:
- **Ice to Water (or Water to Ice)**: This is a change of state from solid to liquid (and vice versa). It is a physical change.
- **Conclusion**: This is a physical equilibrium.

4. **Analyze Option 2**:
- **I2 Solid to I2 Gas**: This represents the sublimation of iodine from solid to gas. It is also a change of state without changing the chemical identity of iodine.
- **Conclusion**: This is a physical equilibrium.

5. **Analyze Option 3**:
- **Sulfur Liquid to Sulfur Gas**: This is a phase change from liquid sulfur to gaseous sulfur. Again, it is a physical change.
- **Conclusion**: This is a physical equilibrium.

6. **Analyze Option 4**:
- **SO2 to 2 O3**: This represents a chemical reaction where sulfur dioxide (SO2) is converted into ozone (O3). This process involves a change in the chemical identity of the substances involved.
- **Conclusion**: This is not a physical equilibrium.

7. **Final Answer**:
- The option that is not a physical equilibrium is **Option 4 (SO2 to 2 O3)**.