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 rate-determining 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?

Reactivity 2.2.7

Understandings:

Understandings:

**Energy profiles can be used to show the activation energy and transition state of the rate-determining step in a multistep reaction.**

- Construct and interpret energy profiles from kinetic data.

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”.

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”?

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?

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.

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.