The temperature coefficient of a reaction is :

Options

A. The ratio of the rate constants of two reactions at `25^@C`
B. The ratio of the rate constants of a reaction at `25^@C and 35^@C`
C. The ratio of the rate constants at any two different temperature
D. None of the above

Answer

To determine the temperature coefficient of a reaction, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition**: The temperature coefficient of a reaction (often denoted as \( Q_{10} \)) is defined as the ratio of the rate constants of a reaction at two different temperatures, specifically when the temperature difference is 10 degrees Celsius.

2. **Identify the Formula**: The formula for the temperature coefficient can be expressed as:
\[ Q_{10} = \frac{k_{T + 10}}{k_T} \]
where \( k_{T + 10} \) is the rate constant at temperature \( T + 10 \) °C and \( k_T \) is the rate constant at temperature \( T \) °C.

3. **Choose the Temperature Range**: In this case, we typically consider a temperature range of 25 °C to 35 °C. Therefore, we can set:
- \( T = 25 \) °C
- \( T + 10 = 35 \) °C

4. **Apply the Formula**: Substitute the temperatures into the formula:
\[ Q_{10} = \frac{k_{35}}{k_{25}} \]

5. **Interpret the Coefficient**: It is commonly observed that the rate of many reactions approximately doubles or triples with every 10 °C increase in temperature. This means:
- If \( Q_{10} \approx 2 \), the reaction rate doubles.
- If \( Q_{10} \approx 3 \), the reaction rate triples.

6. **Select the Correct Option**: Based on the information provided, the correct answer is likely found in option B, which discusses the ratio of the rate constants at 25 °C and 35 °C.

### Final Answer:
The temperature coefficient of a reaction is defined as the ratio of the rate constants at two temperatures, specifically at a 10 °C difference. In this case, the correct option is B.

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