1. reactants products

2. OUTCOME QUESTION(S): C12-3-06 REACTION RATES Vocabulary & Concepts
Formulate an operational definition of reaction rate and solve rate problems.
Include: average rate, instantaneous rates
Relate the rate of formation of a product to the rate of disappearance of a reactant given experimental rate data and reaction stoichiometry.
Use the Collision Theory to explain the rate of chemical reactions.
Include: Activation energy
Vocabulary & Concepts

3. The key is a measurement taken over time
Kinetics
Branch of chemistry that studies:
Speed or rate that a species / reaction changes.
2. Steps or mechanism, of a reaction.
Some reactions do not occur in one simple step, some occur in as a series of steps creating a complex reaction
Rate can be found by measuring different properties/variables - depending on the reaction:
Concentration (mol/L·s)
Temperature (°C/min)
Pressure (kPa/h)
Mass (g/s)
Colour, pH, conductivity…
The key is a measurement taken over time

4. A(s) + B(l) C(g) + heat Rate = Measured change in a property
change in energy
A(s) + B(l) C(g) heat
change in mass
change in pressure
We will use concentrations most of the time
Rate = Measured change in a property
Time for change to occur
Average Rate is described as total change in concentration over time.
RateP = Δ[P] Δt
slow
Final
RateP = [P]final - [P]initial
tfinal - tinitial
Average (secant)
fast
Initial
All reactions have quick initial rates, but slow down over time

5. Units will match those given in the table
a. What is rate of production of B over the 50 seconds?
Initial
RateB = Δ[B] Δt
Final
RateB = [B]final - [B]initial
tfinal - tinitial
RateB = [0.67]f - [0.0]i
50.0f - 0.0i
Units will match those given in the table
RateB = mol/L·s
moles per litre per second

6. b. What is the production rate for interval 20 s to 40 s?
Initial
RateB = Δ[B] Δt
Final
RateB = [B]final - [B]initial
tfinal - tinitial
RateB = [0.65]f - [0.50]i
40.0f i
RateB = mol/L·s

7. Decomposition of nitrogen dioxide produces nitrogen monoxide and oxygen:
2 NO2 (g) NO (g) O2 (g)
Time (min)
[NO2] (mol/L)
[NO] (mol/L)
[O2] (mol/L)
0.0
0.100
0.00 10
0.066
0.034
0.017 20
0.048
0.052
0.026 30
0.038
0.062
0.031 40
0.030
0.070
0.035
Notice the rates are slowing down over time
Notice reactants are decreasing and products are increasing

8. – a. Ave. rate of decomposition of NO2 over 40 min.
Time (min)
[NO2] (mol/L)
[NO] (mol/L)
[O2] (mol/L)
0.0
0.100
0.00 10
0.066
0.034
0.017 20
0.048
0.052
0.026 30
0.038
0.062
0.031 40
0.030
0.070
0.035
Negative rate equation communicates decrease with time
Rate = 1.75 x 10-3 mol/L·min
RateNO2 = Δ[NO2] Δt –
Rate value will always be expressed as a positive value
Rate = – [0.030]f - [0.100]i
40f - 0i
Rate = – ( – )

9. Notice rate equation is a positive value – increasing with time
b. Ave. rate of production of O2 over 40 min.
Time (min)
[NO2] (mol/L)
[NO] (mol/L)
[O2] (mol/L)
0.0
0.100
0.00 10
0.066
0.034
0.017 20
0.048
0.052
0.026 30
0.038
0.062
0.031 40
0.030
0.070
0.035
RateO2 = Δ[O2] Δt
Notice rate equation is a positive value – increasing with time
Rate = [0.035]f - [0.00]i
40f - 0i
Notice the relationship between the values of O2 and the previous rate of NO2?
Rate = x 10-4 mol/L·s

10. How is the rate calculated for a specific time?
2 NO2 (g) NO (g) O2 (g)
How is the rate calculated for a specific time?
Time (min)
[NO2] (mol/L)
[NO] (mol/L)
[O2] (mol/L)
0.0
0.100
0.00 10
0.066
0.034
0.017 20
0.048
0.052
0.026 30
0.038
0.062
0.031 40
0.030
0.070
0.035
We still need a “final” and “initial” point, so we must extend the point and create a line

11. As opposed to over an interval of time
Instantaneous rate - rate at a specific point in time.
Determined by calculating the slope of the line tangent to a point on the curve.
As opposed to over an interval of time
RateNO2 = [NO2]final - [NO2]initial
tfinal - tinitial
Think of it as extending the point in both directions to create a line that estimates the rate at that moment
[NO2]f
(tangent)
[NO]i ti tf

12. Rates can be predicted from reaction stoichiometry.
2 NO2 (g) NO (g) O2 (g)
How does the graph match the information of the equation?

13. What is the rate of production of O2 and the rate of disappearance of NO2 if NO is made at a rate of 0.60 mol/Ls?
2 NO2 (g) NO (g) O2 (g)
Look at the equation and try to predict the value before attempting to solve
0.60 mol/L·s NO
2 mol NO
1 mol O2
= mol/L·s O2
0.60 mol/L·s NO
2 mol NO
2 mol NO2
= mol/L·s NO2

14. 2 N2O5 (g) NO2 (g) O2 (g)
The rate of N2O5 is half the rate of NO2
The rate of O2 is half the rate of N2O5
The rate of NO2 is 4x the rate of O2
Reaction Rate – numerical value of ANY reactant or product change, equalized to a coefficient of 1.
Rate of the reaction is a consistent value regardless of which species is investigated - all values are equivalent and give same reaction rate value

15. aA + bB cC 2 N2O5 (g) 4 NO2 (g) + 1 O2 (g) Reaction Rate _ 1 Δ[A] a Δt
b Δt
1 Δ[C]
c Δt
1 Δ[D]
d Δt
RateReaction = = = = +
2 N2O5 (g) NO2 (g) O2 (g)
_ 1 Δ[N2O5]
2 Δt
1 Δ[NO2]
4 Δt
Δ[O2] Δt
RateReaction = = = +
The equations all give a consistent value for the rate of the reaction at that time interval

16. CAN YOU / HAVE YOU? C12-3-06 REACTION RATES Vocabulary & Concepts
Formulate an operational definition of reaction rate and solve rate problems.
Include: average rate, instantaneous rates
Relate the rate of formation of a product to the rate of disappearance of a reactant given experimental rate data and reaction stoichiometry.
Use the Collision Theory to explain the rate of chemical reactions.
Include: Activation energy
Vocabulary & Concepts