Essential ideas
 Rate expressions can only be determined empirically and these limit possible reaction mechanisms. In particular cases, such as a linear chain of elementary reactions, no equilibria and only one significant activation barrier, the rate equation is equivalent to the slowest step of the reaction.
 The activation energy of a reaction can be determined from the effect of temperature on reaction rate.
16.1 Rate expressions and orders of reaction

Understandings:
The order of a reaction can be either integer or fractional in nature. The order of a reaction can describe, with respect to a reactant, the number of particles taking part in the ratedetermining step. Applications and skills: Deduction of the rate expression for an equation from experimental data and solving problems involving the rate expression. 
16.1 Ratedetermining step

Understandings:
Reactions may occur by more than one step and the slowest step determines the rate of reaction (rate determining step/RDS). 
16.1 Energy level profiles

This video shows how to identify the transition states and intermediates in an energy level profile.

16.1 Molecularity

Understandings:
The molecularity of an elementary step is the number of reactant particles taking part in that step. 
16.1 Reaction mechanism

This video covers how to deduce to the overall equation from the reaction mechanism and also how to deduce the rate expression from the elementary steps.
Please note that the last example is termolecular, not bimolecular as stated in the video. 
16.1 Sketch, identify and analyse graphical representations for zero, first and secondorder reactions.

Applications and skills:
Sketching, identifying, and analysing graphical representations for zero, first and second order reactions. 
16.2 The Arrhenius equation
Note that the IB definition of the Arrhenius constant (A) indicates the frequency of collisions and the probability that collisions have proper orientations.

Understandings:
The Arrhenius equation uses the temperature dependence of the rate constant to determine the activation energy. A graph of 1/T against ln k is a linear plot with gradient – Ea / R and intercept, lnA. The frequency factor (or preexponential factor) (A) takes into account the frequency of collisions with proper orientations. Applications and skills: Analysing graphical representation of the Arrhenius equation in its linear form Using the Arrhenius equation 
16.1 Catalysts

Understandings:
Catalysts alter a reaction mechanism, introducing a step with lower activation energy. Guidance: Catalysts are involved in the ratedetermining step. 
16.2 Effect of temperature in the rate constant k

Applications and skills:
Describing the relationships between temperature and rate constant; frequency factor and complexity of molecules colliding. 