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WalesChemistryQuick questions
Unit 3: Physical and Inorganic Chemistry
Quick questions on Chemical kinetics - WJEC A-Level Chemistry
7short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is determining orders from initial-rate data?Show answer
The cleanest way to find an order is the initial-rates method: run several experiments changing one concentration at a time and compare the initial rates. If doubling a concentration leaves the rate unchanged, that reactant is zero order; if the rate doubles, first order; if it quadruples, second order. Comparing two experiments where only one concentration differs isolates the effect of that reactant. Once all orders are known, substitute one full set of data into the rate equation to find the rate constant , then derive its units from the overall order.
What is mechanism of nucleophilic substitution?Show answer
Whether a halogenoalkane reacts by a one-step or two-step pathway is revealed by its order: first order overall points to a rate-determining ionisation, second order to a single concerted step. Enzyme kinetics. At high substrate concentration enzyme reactions become zero order because the enzyme is saturated, an everyday example of order changing with conditions.
What is q1?Show answer
State what is meant by the order of a reaction with respect to a reactant. [1 mark]
What is q2?Show answer
Give the units of the rate constant for a second-order reaction. [1 mark]
What is q3?Show answer
State what a constant half-life tells you about the order. [1 mark]
What is q4?Show answer
A reaction is first order in X and second order in Y. State the overall order. [1 mark]
What is q5?Show answer
Explain why a zero-order reactant does not appear in the rate equation. [1 mark]
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