Question

The units of rate constants of two reactions I and II are respectively mol\(^{-1}\) L s\(^{-1}\) and mol L\(^{-1}\)s\(^{-1}\). Then,

• A. reaction I is first order and reaction II is second order.
• B. reaction I is second order and reaction II is first order.
• C. reaction I is first order and reaction II is zero order.
• D. reaction I is zero order and reaction II is first order.
• E. reaction I is second order and reaction II is zero order.

Hint:

Zero order units match the rate units (\(\text{mol L}^{-1}\text{s}^{-1}\)).
First order units are simply \(\text{s}^{-1}\).
Second order units involve \(\text{M}^{-1}\text{s}^{-1}\) (or \(\text{L mol}^{-1}\text{s}^{-1}\)).

Answer 1

Answer: (E)

Step 1: Understanding the Concept:
The units of the rate constant (\(k\)) depend on the overall order of the reaction (\(n\)).

Step 2: Key Formula or Approach:
The general unit for a rate constant of order \(n\) is:
\[ \text{Units of } k = (\text{mol L}^{-1})^{1-n} \text{ s}^{-1} \]

Step 3: Detailed Explanation:
- For Reaction I: The unit is \(\text{mol}^{-1} \text{ L s}^{-1}\).
Comparing this to the formula: \((1-n) = -1 \implies n = 2\).
Therefore, Reaction I is second order.
- For Reaction II: The unit is \(\text{mol L}^{-1} \text{ s}^{-1}\).
Comparing this to the formula: \((1-n) = 1 \implies n = 0\).
Therefore, Reaction II is zero order.

Step 4: Final Answer:
Reaction I is second order and Reaction II is zero order.