Reactivity 2.2 How fast? The rate of chemical change (HL)
Reactivity 2.2.6
Understandings:
Understandings:
 Many reactions occur in a series of elementary steps. The slowest step determines the rate of the reaction.
 Evaluate proposed reaction mechanisms and recognise intermediates.
 Distinguish between intermediates and transition states, and recognise both in energy profiles of reactions.
 Include examples where the ratedetermining step is not the first step.
 Proposed reaction mechanisms must be consistent with kinetic and stoichiometric data.
 Reactivity 3.4 Which mechanism in the hydrolysis of halogenoalkanes involves an intermediate?

This video covers rate expressions.


This video covers transition states.

Reactivity 2.2.7
Understandings:
Understandings:
 Energy profiles can be used to show the activation energy and transition state of the ratedetermining step in a multistep reaction.
 Construct and interpret energy profiles from kinetic data.

This video covers energy level profiles for multistep reactions.

Reactivity 2.2.8
Understandings:
Understandings:
 The molecularity of an elementary step is the number of reacting particles taking part in that step.
 Interpret the terms “unimolecular”, “bimolecular” and “termolecular”.

This video covers molecularity.

Reactivity 2.2.9
Understandings:
Understandings:
 Rate equations depend on the mechanism of the reaction and can only be determined experimentally.
 Deduce the rate equation for a reaction from experimental data.


Reactivity 2.2.10
Understandings:
Understandings:
 The order of a reaction with respect to a reactant is the exponent to which the concentration of the reactant is raised in the rate equation.
 The order with respect to a reactant can describe the number of particles taking part in the rate determining step.
 The overall reaction order is the sum of the orders with respect to each reactant.
 Sketch, identify and analyse graphical representations of zero, first and second order reactions.
 Concentration–time and rate–concentration graphs should be included.
 Only integer values for order of reaction will be assessed.
 Tool 1, 3, Inquiry 2 What measurements are needed to deduce the order of reaction for a specific reactant?
 Nature of science Why are reaction mechanisms only considered as “possible mechanisms”?

This video covers orders of reaction.


This video covers graphical representations of zero, first and secondorder reactions.

Reactivity 2.2.11 and 2.2.12
Understandings:
Understandings:
 The rate constant, k, is temperature dependent and its units are determined from the overall order of the reaction.
 The Arrhenius equation uses the temperature dependence of the rate constant to determine the activation energy.
 Solve problems involving the rate equation, including the units of k.
 Describe the qualitative relationship between temperature and the rate constant.
 Analyse graphical representations of the Arrhenius equation, including its linear form.
 The Arrhenius equation and its linear form are given in the data booklet.
 Reactivity 3.4 What are the rate equations and units of k for the reactions of primary and tertiary halogenoalkanes with aqueous alkali?

This video coves the effect of temperature on the rate constant k.


Reactivity 2.2.12
Understandings:
Understandings:
 The Arrhenius equation uses the temperature dependence of the rate constant to determine the activation energy.
 Describe the qualitative relationship between temperature and the rate constant.
 Analyse graphical representations of the Arrhenius equation, including its linear form.
 The Arrhenius equation and its linear form are given in the data booklet.

This video covers the Arrhenius equation.

Reactivity 2.2.13
Understandings:
Understandings:
 The Arrhenius factor, A, takes into account the frequency of collisions with proper orientations.
 Determine the activation energy and the Arrhenius factor from experimental data.

This video covers how to determine the activation energy for a reaction.
