1. Kinetics Topic 6

2. Rate of reactions can be fast or slow
defined as the change in [concentration] of the reactants or products per time
concentration of reactants decreases over time
[reactants]/time
concentration of products increase over time
[products]/time
normally measure in Molarity per sec (M/s)
will continue until reaches equilibrium or one of the reactants is used up
concentration is analogous to volume or mass changing over time

3. concentration of reactants decrease over time
concentration of products increase over time
(reactants)

4. Experiments for measuring rate of reactions
over time, could measure the change of:
for gaseous reactions
mass would go down as gas escapes
volume would increase at constant temp. and pressure
pressure would increase at constant temp. and volume
change in pH if acids and bases are involved
change in temperature
change in electrical conductivity
if produces ions in solution, conductivity will increase
using a spectrometer to detect color changes

6. Analyzing data from rate experiments (Concentration, Volume, and Mass)
usually involves a graph of properties over time
usually a curve, and the reaction rate is determined from the slope of the line at a time (also known as a tangent)
reaction rates tend to slow with time as reactants are converted to products

7. Example C4H9Cl(aq) + H2O(l)  C4H9OH(aq) + HCl(aq)
reaction slows down with time because the Concentration of the reactants decreases
“rise over run”
.040M/200s
= .0002M/s
.025M/400s
= M/s

9. the change in concentration of a reactant or product per unit of time
[ ] refer to the concentration of the reactants or products

10. 2NO2(g)  2NO(g) + O2(g)
product
[NO2] t
[NO2]
product t
reactant

11. reaction is creating gas so Volume increases over time
gas is being released in the reaction so Mass decreases over time

13. Kinetic theory
the average energy of particles is proportional to the temperature (Kelvin or Celsius)
all particles have same energy if the same temperature
ex. 4He 20Ne Ar
would all have the same temp. and energy
however, lighter particles (4He) would have greatest speed than larger particles given the same energy
𝐾𝐸=1/2𝑚𝑣2

14. Activation Energy Ea
a minimum amount of energy required for reaction to occur
bonds need to be broken first
the molecules must posses sufficient energy to get over the activation energy barrier.

15. Collision theory in order for particles to react
particles must collide
must collide in the correct orientation/angle
must collide with enough kinetic energy to overcome the activation energy (E > Ea)
if the previous conditions are “enough”, particles can overcome the activation energy and reaction will occur
meaning the bonds holding the reactants together will be broken and the reaction can take place

17. Factors That Affect Reaction Rates
any factor that increases the frequency of collisions or increases the energy with which particles collide will make the reaction go faster:
temperature
pressure (gas only)
surface area
concentration
catalysts

18. 1. Temperature increase temp
increases number of collisions per unit time
reaction rate approximately doubles for each 10oC or K rise in temperature
increases energy of the collisions
greater chance E > Ea
will not “help with” geometry

19. 2. Pressure only for gasses
reducing volume while keeping temp constant increases the reaction rate
forcing them together will increase number of collisions per unit time
will not “help with” geometry and energy

20. 3. Surface area
smaller particles have more surface area and will increase the reaction rate
more collisions per unit time
will not “help with” geometry and energy

24. 4. Concentration
increasing concentration will increase the reaction rate by increasing more collisions per unit time
will not “help with” geometry and energy

26. 5. Catalysts lowers the activation energy (Ea) for the reaction
provide an alternate reaction (rxn) pathway
increase the rate of a reaction
are not used up or chemically changed in the reaction

28. Maxwell–Boltzman energy distribution curve

29. another way to look at how many particles can react
area under the curve shows the number of gas particles
the # of particles remains constant
not all gas particles have the same energy
only some gas particles (blue area) have enough energy to react

30. The affect of temperature

33. the area under the curve remains the same because the number of particles doesn't change
higher temps. shifts the curve to the right (therefore, the peek must be lower) resulting in an increase in collision frequency and thus more successful collisions

34. The affect of a catalyst

35. Never move the new activation energy to the left of the peak
Never move the new activation energy to the left of the peak. Catalysts don’t help out that much!