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Rate equations (A-level only)
This A-level-only topic makes reaction-rate analysis quantitative.
9
Objectives
10
Flashcards
10
Questions
90 min
Study time
AqaA LevelChemistryPhysical chemistry
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Syllabus checklist
What you need to know
9 objective pages available
Rate equations and orders (A-level only)5 objectives
- Deduce orders of reaction from initial rate data.
- Write rate equations using experimentally determined orders.
- Calculate rate constants and their units.
- Use half-life evidence for first-order reactions.
- Interpret concentration-time graphs.
Mechanisms and rate-determining steps (A-level only)4 objectives
- Explain the rate-determining step in a mechanism.
- Use a proposed mechanism to predict a rate equation.
- Use a rate equation to assess whether a proposed mechanism is consistent with data.
- Distinguish overall equation from rate-determining step.
Key terms
Rate constant (k)Order of reactionRate of reactionRate lawRate equationReaction orderRate-determining stepMechanismActivation energyIntermediates
Exam tips
- Show all workings in calculations: Always show your calculations step-by-step, including units and significant figures.
- Carefully analyze the rate equation: Always check the units of k and ensure they match the expected units based on the order of the reaction.
Common mistakes
- Confusing rate constant with rate: Remember that the rate constant is a fixed value for a given reaction at a specific temperature, while the rate can change based on reactant concentrations.
- Incorrectly identifying the order of a reaction: Remember that the order must be determined experimentally and is not necessarily related to the stoichiometric coefficients.
Practice preview
- Which of the following statements about the rate of a reaction is true?
- Given the following initial rate data for the reaction A + B → C, determine the order of reaction with respect to A if doubling the concentration of A doubles the rate of reaction.
- For the reaction 2A + B → 3C, the following initial rates were observed: - [A] = 0.1 M, [B] = 0.1 M, Rate = 0.02 M/s - [A] = 0.2 M, [B] = 0.1 M, Rate = 0.08 M/s Determine the order of reaction with respect to B.
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