AP Chemistry Unit Review
Unit 5: Kinetics
How it applies to our lives
In modern airbags, there is a multistep reaction that occurs with the decomposition of solid sodium azide. The crash sensor ignites only when there is a sudden drop in the car's momentum. When the temperature rises, the chemical bonds of sodium azide break, forming nitrogen gas. The deployment of an airbag demonstrates how fast particles break apart and react resulting in the rapid production of nitrogen gas. Hence, the nitrogen gas is ultimately used to reduce the impact force created by the crash.
Key Vocabulary
Select a card to reveal its definition.
Kinetics
Rate determining step
Collision Theory
Catalyst
Elementary Step
Reaction Energy Profile
Main Takeaways
Rate increased when a solid is broken into pieces (increase in surface area), higher concentration of reactants (more particles will experience frequent collisions), high temperature (high average kinetic energy, more likely for particles to move quicker and overcome energy barrier, adding a catalyst (directly providing an alternative pathway requiring a lower activation energy for reaction to proceed, decreasing the volume of the container if the reaction involves gases.) (particles are closer together, more particles will experience frequent collisions).
In a multistep reaction mechanism, to find if a reaction mechanism matches , then you need to test it experimentally.
The overall balanced chemical reaction (not to be confused with overall rate → points to the rate law of the rate determining step) can be found from the reaction mechanism by adding up the steps and eliminating catalysts and intermediates.
To figure out what order given a [M] vs time, ln[M] vs time, or 1/[M] vs time graph, the order can be evaluated wherever a linear line appears within one of these given graphs.
The rate constant of a 0th order reaction is equal to the negative slope of the line graph.
Common Misconceptions
The student may think that the rate determining step will keep both intermediates and catalysts, however the slow step can include catalysts but must eliminate any intermediates if the previous step is a fast equilibrium to derive the rate law.
Unit Quiz
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