Question

If the unit of specific rate constant (\(k\)) for a certain gaseous reaction is atm\(^{-2}\) s\(^{-1}\), then the order of the reaction is-

• A. Zero order
• B. First order
• C. Second order
• D. Third order

Hint:

For gaseous reactions, compare pressure units in the rate law to determine the order of reaction.

Answer 1

The Correct Option is D

Step 1: For a gaseous reaction, the rate law can be written in terms of pressure: \[ \text{Rate} = k (P)^n \]
Step 2: The unit of rate is atm s\(^{-1}\). Given unit of \(k = \text{atm}^{-2}\,\text{s}^{-1}\).
Step 3: Substituting units: \[ \text{atm s}^{-1} = (\text{atm}^{-2}\,\text{s}^{-1})(\text{atm})^n \]
Step 4: Comparing powers of atm: \[ -2 + n = 1 \quad \Rightarrow \quad n = 3 \]
Step 5: Hence, the reaction is of third order.