Kinetics- Study Guide
1. The collision theory
a. Explains why reactions occur between atoms, ions, and/or molecules
and allows us to predict what conditions are necessary for a successful
reaction to take place:
i. Particles must collide
ii. Must have proper orientation
iii. Must collide with sufficient energy to break bonds
b. Relates to the kinetic energy of particles as they collide.
c. The total number of collisions per second is known as the collision
frequency.
d. With increasing temperature, the kinetic energy of the particles and
the number of particles with energy greater than the activation energy
increases.
2. Energy diagrams as related to
kinetics:
a. Particles need to overcome the
activation energy in order to
react. Only particles with energy
equal to or greater than this
activation energy value will react.
b. Transition state is the point at the peak on the energy diagram (top of
activation energy hump).
3. Rate of reaction: change in a concentration of reactant or product over time
(units= M/s)
a. Rate of reaction slows down with time because concentrations
decrease.
b. Instantaneous rate vs average rate
i.
Instantaneous is the rate at one specific time. It can be
calculated by finding the slope of the tangent line.
ii.
Initial reaction rate is an example of instantaneous rate.
iii.
Average rate is the rate of the overall reaction. The rate
between 2 specified points. Calculate 2 ways. Slope of secant
line OR change in concentration over change in time.
c. Temperature positively affects rate as particles get more energy to
overcome the activation energy. Particles also move faster and
therefore the frequency of collisions increases.
d. Concentration positively affects rate as there are more particles so
the frequency of collisions increases.
e. Surface area. For a solid, only the particles on the surface can react.
Increase surface area, increase rate because more particles can react.
f. Nature of reactants. Ionized solutions react very fast. Complex ions
take longer to react as more bonds would need to be broken.
i.
Two gases together would react very fast too.
ii.
Solids to gases, rate increases as molecules become more
free to collide and react.
g. Catalysts can also speed up the reaction by providing an alternate
pathway which requires less activation energy.