R2.2 How fast? The rate of chemical change (HL)
15 revision questions with answers for R2.2 How fast? The rate of chemical change (HL). Read them here, or play the set as a class game on the projector. Free to host, and students join with a code.
Overall order of reaction for rate = k[A]²[B]?
- 2
- 1
- 3Right answer
- 4
What this set covers
Rate at HL: rate equations, order of reaction, units of the rate constant, half-life of first-order reactions, mechanisms with rate-determining steps and intermediates, and the Arrhenius equation and its plot.
- Common mix-up
- Students often confuse order with molecularity: order comes from the rate equation, while molecularity counts the particles colliding in one elementary step.
- Revision tip
- Derive the units of k for zero, first and second order from rate = k[A]ⁿ, then sketch an Arrhenius plot and label the gradient and intercept.
All 15 questions and answers
Overall order of reaction for rate = k[A]²[B]?
Answer: 3
Doubling [A] quadruples the rate. Order with respect to A?
Answer: 2
Doubling [B] leaves the rate unchanged. Order with respect to B?
Answer: 0
Units of the rate constant for a first-order reaction?
Answer: s⁻¹
Units of the rate constant for a second-order reaction?
Answer: dm³ mol⁻¹ s⁻¹
The rate constant of a given reaction increases with…?
Answer: Temperature
Half-life of a first-order reaction is…?
Answer: Independent of concentration
First-order reaction with a 10 s half-life: fraction of reactant left after 30 s?
Answer: 1/8
Slowest elementary process in a reaction mechanism?
Answer: Rate-determining step
Number of particles that collide in an elementary step?
Answer: Molecularity
Species formed in one step of a mechanism and used up in a later step?
Answer: Intermediate
For NO₂ + CO → NO + CO₂, rate = k[NO₂]². Reactants in the slow step?
Answer: 2NO₂
The Arrhenius equation?
Answer: k = Ae^(−Eₐ/RT)
Gradient of an Arrhenius plot of ln k against 1/T?
Answer: −Eₐ/R
Intercept of an Arrhenius plot of ln k against 1/T?
Answer: ln A
Play it as a class game
Play this set opens it in splycr, where you can host it for your class straight away. Hosting needs no account: put the room code on the projector, and students join from a phone with the code and their first name. Each question plays as multiple choice, and the three wrong options were written for that question.