Which one of the following is not a first order reaction?

Options

A. `CH_(3)COOCH+H_(2)Ooverset(H^(+))rarrCH_(3)OH`
B. `CH_(3)COOCH_(2)H_(5)+NaOHrarrCH_(3)COONa+C_(2)H_(5)OH`
C. `2H_(2)O_(2)rarr 2H_(2)O+O_(2)`
D. `2N_(2)O_(5)rarr4NO_(2)+O_(2)`

Answer

To determine which of the given options is not a first-order reaction, we need to analyze each option based on the definition of first-order reactions. A first-order reaction is characterized by the fact that the rate of reaction depends on the concentration of only one reactant.

### Step-by-Step Solution:

1. **Understand the Definition of First-Order Reactions**:
- A first-order reaction is one where the rate of reaction is directly proportional to the concentration of one reactant. This means that if you change the concentration of that reactant, the rate of reaction will change accordingly.

2. **Analyze Option A: CH3COOH**:
- In this reaction, acetic acid (CH3COOH) reacts with water (H2O) to produce H+ ions. The rate of reaction depends primarily on the concentration of acetic acid, as water is in excess and does not affect the rate significantly. Therefore, this is a first-order reaction.

3. **Analyze Option B: CH3COOCH2 and NaOH**:
- This reaction involves both CH3COOCH2 and NaOH. Here, both reactants contribute to the rate of reaction. The rate depends on the concentrations of both CH3COOCH2 and NaOH, indicating that this is not a first-order reaction but a second-order reaction.

4. **Analyze Option C and D**:
- Both options C and D involve two-step processes where one step is fast and the other is slow. In such cases, the rate-determining step is the slow step, which typically involves only one reactant. Thus, both options C and D can still be classified as first-order reactions.

5. **Conclusion**:
- Based on the analysis, option B (CH3COOCH2 and NaOH) is the only one that does not qualify as a first-order reaction because the rate depends on the concentration of more than one reactant.

### Final Answer:
**Option B is not a first-order reaction.**

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