R2.2 (AHL) How Fast? The Rate of Chemical Change

How can the rate of a reaction be controlled?

R2.2 (AHL) How Fast? The Rate of Chemical Change.pptx

Skills Focus

Experimental Techniques: Measuring variables: understand to accurately measure to an appropriate level of precision: mass, volume, pH and time.
Applying techniques: colorimetry or spectrophotometry
Controlling Variables: calibrate measuring apparatus (calorimeter)
Controlling Variables: maintain constant environmental conditions of systems
Technology: Applying technology to collect data: use sensors.
Technology: Applying technology to process data: represent data in a graphical form.
Graphing: Sketch graphs, with labelled but unscaled axes, to qualitatively describe trends.
Graphing: Construct and interpret tables, charts and graphs for raw and processed data including bar charts, histograms, scatter graphs and line and curve graphs.
Graphing: Extrapolate and interpolate graphs.

UNDERSTANDINGS

R2.2.6 (AHL) —Many reactions occur in a series of elementary steps. The slowest step determines the rate of the reaction.
- Evaluate proposed reaction mechanisms and recognize reaction intermediates.
- Distinguish between intermediates and transition states, and recognize both in energy profiles of reactions.
R2.2.7 (AHL)—Energy profiles can be used to show the activation energy and transition state ofVthe rate-determining step in a multistep reaction.
- Construct and interpret energy profiles from kinetic data.
R2.2.8 (AHL) —The molecularity of an elementary step is the number of reacting particles taking part in that step.
- Interpret the terms “unimolecular”, “bimolecular” and “termolecular”.
R2.2.9 (AHL) —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.
R2.2.10 (AHL) —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 ratedetermining step.
- The overall reaction order is the sum of the orders with respect to each reactant.
R2.2.11—The rate constant, k, is temperature dependent and its units are determined from the overall order of the reaction.
- Solve problems involving the rate equation, including the units of k.
R2.2.12—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.
R2.2.13—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.

MAKING CONNECTIONS

Reactivity 3.4—Which mechanism in the hydrolysis of halogenoalkanes involves an intermediate?

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 3.4—What are the rate equations and units of k for the reactions of primary and tertiary halogenoalkanes with aqueous alkali?