Units of rate constant depend upon

Options

A. temperature
B. time
C. Order of reaction
D. none

Explanation

To determine how the units of the rate constant depend on various factors, we can analyze the relationship between the order of the reaction and the units of the rate constant (k).

### Step-by-Step Solution:

1. **Understanding the Rate Constant (k)**:
The rate constant (k) is a proportionality factor in the rate equation of a chemical reaction. Its units vary depending on the order of the reaction.

2. **General Expression for the Rate Constant**:
The unit of the rate constant for an nth order reaction can be expressed as:
\[ k = \text{(concentration)}^{(1-n)} \cdot \text{(time)}^{-1} \]
where concentration is typically in moles per liter (mol/L) and time is in seconds (s).

3. **Zero Order Reaction**:
For a zero-order reaction (n = 0):
\[ k = \text{(mol/L)}^{(1-0)} \cdot \text{s}^{-1} = \text{mol/L} \cdot \text{s}^{-1} \]
Thus, the unit of k for a zero-order reaction is **mol/L·s**.

4. **First Order Reaction**:
For a first-order reaction (n = 1):
\[ k = \text{(mol/L)}^{(1-1)} \cdot \text{s}^{-1} = \text{s}^{-1} \]
Thus, the unit of k for a first-order reaction is **s⁻¹**.

5. **Second Order Reaction**:
For a second-order reaction (n = 2):
\[ k = \text{(mol/L)}^{(1-2)} \cdot \text{s}^{-1} = \text{(mol/L)}^{-1} \cdot \text{s}^{-1} = \text{L/(mol·s)} \]
Thus, the unit of k for a second-order reaction is **L/(mol·s)**.

6. **Conclusion**:
From the above analysis, we can conclude that the units of the rate constant depend on the order of the reaction. Therefore, the correct answer to the question is that the units of the rate constant depend on the **order of the reaction**.

### Final Answer:
The units of the rate constant depend upon the **order of the reaction**.

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