Question detail
If the rate constant (k) for a second-order reaction is 0.2 dm^3/mol/s, what are the units of the rate constant (A-level cue 95ace33d focus)
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Rate equations (A-level only)
Question
- A. dm^3/mol/s
- B. s^-1 (A-level cue 95ace33d distractor 1)
- C. mol/dm^3/s (A-level cue 95ace33d distractor 2)
- D. g/dm^3 (A-level cue 95ace33d distractor 3)
Answer
dm^3/mol/s
Explanation
The correct option is dm^3/mol/s. dm^3/mol/s is correct because it supports the objective: Calculate rate constants and their units.. The reasoning stays within Rate equations and orders (A-level only) and avoids drifting into a similar A-Level Chemistry idea. This version is uniquely anchored to Rate equations and orders (A-level only). Retrieval anchor: A-level cue 95ace33d. This item is treated as conceptual revision rather than a formal calculation item because the validated answer is an explanation or option choice, not a worked numerical response.
Common mistake
Incorrect Units for Rate Constant
Students often forget to include the correct units for the rate constant when calculating it from a rate equation.
To calculate the rate constant (k), use the formula k = rate / [A]^m[B]^n, where [A] and [B] are the concentrations of the reactants raised to their respective orders. For a second-order reaction, the units of k will be dm^3 mol^-1 s^-1. Always ensure to include units in your final answer. For example, if the rate is 0.1 mol/dm^3/s and the concentrations are 0.2 mol/dm^3 and 0.3 mol/dm^3 with orders 1 and 1 respectively, substitute: k = 0.1 / (0.2^1 * 0.3^1) = 0.1 / 0.06 = 1.67 dm^3 mol^-1 s^-1.
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