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Unit 5: Kinetics

11 dot points across 11 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How does a catalyst speed a reaction without being consumed, and what kinds of catalysis are there?

Topic 5.11 Catalysis: explain how a catalyst increases the rate by providing an alternative pathway with a lower activation energy, and distinguish homogeneous, heterogeneous and enzyme catalysis.
A focused answer to AP Chemistry Topic 5.11, covering how a catalyst lowers the activation energy by offering an alternative mechanism, the types of catalysis (homogeneous, heterogeneous, enzymatic), and why a catalyst leaves enthalpy and equilibrium unchanged, with full worked examples.
10 min answer →

Why does temperature have such a large effect on reaction rate, and how does the collision model and the Arrhenius equation explain it?

Topic 5.5 Collision Model: use collision theory and the Arrhenius equation to explain how activation energy, temperature, orientation and collision frequency control the rate constant.
A focused answer to AP Chemistry Topic 5.5, covering collision theory, activation energy, the Maxwell-Boltzmann distribution, molecular orientation, and the Arrhenius equation linking rate constant to temperature, with full worked examples.
11 min answer →

How does the concentration of a reactant change with time, and how can the shape of that change reveal the reaction order?

Topic 5.3 Concentration Changes Over Time: use the integrated rate laws for zero-, first- and second-order reactions, identify order from a linear plot, and use the half-life of a first-order reaction.
A focused answer to AP Chemistry Topic 5.3, covering the integrated rate laws for zero-, first- and second-order reactions, identifying order from linear plots, and the first-order half-life, with full worked examples.
11 min answer →

What is an elementary reaction, and why can its rate law be written directly from its molecularity?

Topic 5.4 Elementary Reactions: identify the molecularity of an elementary step and write its rate law directly from its stoichiometry, distinguishing elementary steps from overall reactions.
A focused answer to AP Chemistry Topic 5.4, covering elementary reactions, molecularity (unimolecular, bimolecular, termolecular), writing the rate law of an elementary step from its stoichiometry, and why this differs from overall reactions, with full worked examples.
9 min answer →

How does the rate of a reaction depend on the concentrations of the reactants, and how do we find that dependence?

Topic 5.2 Introduction to Rate Law: write the rate law of a reaction, determine the reaction orders and the rate constant from initial-rate data, and interpret the meaning of order and the units of the rate constant.
A focused answer to AP Chemistry Topic 5.2, covering the rate law, reaction order, the rate constant and its units, and how to find orders and k from initial-rate (method of initial rates) data, with full worked examples.
11 min answer →

How is an overall reaction built from a sequence of elementary steps, and what is an intermediate?

Topic 5.7 Introduction to Reaction Mechanisms: represent a reaction as a sequence of elementary steps, identify reaction intermediates and catalysts, and confirm that the steps sum to the overall equation.
A focused answer to AP Chemistry Topic 5.7, covering reaction mechanisms as sequences of elementary steps, identifying intermediates and catalysts, and checking that the steps add up to the overall equation, with full worked examples.
9 min answer →

How does a potential-energy diagram for a multistep reaction show intermediates and identify the rate-determining step?

Topic 5.10 Multistep Reaction Energy Profile: interpret an energy diagram with more than one peak to identify intermediates, the activation energy of each step, and the rate-determining step.
A focused answer to AP Chemistry Topic 5.10, covering multistep potential-energy diagrams, identifying intermediates in the valleys, the activation energy of each step, and locating the rate-determining step from the highest barrier, with full worked examples.
9 min answer →

How do we find the rate law when the slow step of a mechanism follows a fast equilibrium and contains an intermediate?

Topic 5.9 Pre-Equilibrium Approximation: derive the rate law of a mechanism with a fast initial equilibrium followed by a slow step by expressing the intermediate concentration in terms of reactant concentrations.
A focused answer to AP Chemistry Topic 5.9, covering the steady-state and pre-equilibrium approximation, mechanisms with a fast initial equilibrium and a slow second step, and how to eliminate an intermediate to derive the overall rate law, with full worked examples.
10 min answer →

What does a reaction energy profile show about activation energy, the transition state and the enthalpy of reaction?

Topic 5.6 Reaction Energy Profile: interpret a potential-energy diagram to identify the activation energy of the forward and reverse reactions, the transition state and the enthalpy of reaction.
A focused answer to AP Chemistry Topic 5.6, covering the potential-energy diagram, the transition state, the activation energy of the forward and reverse reactions, the relationship to enthalpy of reaction, and the effect of a catalyst, with full worked examples.
10 min answer →

How does the rate-determining step of a mechanism set the rate law of the overall reaction?

Topic 5.8 Reaction Mechanism and Rate Law: identify the rate-determining (slow) step of a mechanism and use it to write the rate law, and check a proposed mechanism against the experimental rate law.
A focused answer to AP Chemistry Topic 5.8, covering the rate-determining step, writing the rate law from the slow step, the slow-step-first case, and how a proposed mechanism must agree with the experimental rate law, with full worked examples.
10 min answer →

How do we define and measure the rate of a chemical reaction, and what controls how fast it goes?

Topic 5.1 Reaction Rates: express the rate of a reaction in terms of the change in concentration of a reactant or product over time, relate rates through the stoichiometric coefficients, and identify the factors that influence rate.
A focused answer to AP Chemistry Topic 5.1, covering the definition of reaction rate, average versus instantaneous rate, relating rates through stoichiometric coefficients, and the factors that change the rate of a reaction, with full worked examples.
10 min answer →