SHS-Chemical Kinetics Part 2 by Canonigo

This presentation discusses the Rate of a Reaction.

5. Time A B
0s 1.00 mol0 mol
20s
40s
0.54 mol
0.30 mol
0.46 mol
0.70 mol
A B
In this reaction, the concentration of A was measured
at various times

6. Tim
e
VioletGreen
20
1
0
0
3
0
50
60
40
50 mol
23 mol
11 mol
5 mol
3 mol
0.1
mol0 mol
0 mol
24 mol
39 mol
45 mol
48 mol
49.5 mol
50
mol

7. A plot of
concentration vs.
time
for this reaction
yields a curve like
this

8. Reaction rates are usually
expressed as the concentration of
reactant consumed or the
concentration of product formed
per unit time. The units are thus
moles per liter per unit time,
written as M/s, M/min, or M/h. To
measure reaction rates, chemists
initiate the reaction
UNIT OF REACTION RATES:
RATE: M/s, M/m M/h

9. The progress of a simple reaction (A → B)
is shown in ; are snapshots of the
composition of the solution at 10 s
intervals. The number of molecules of
reactant (A) and product (B) are plotted
as a function of time in the graph.

10. Each point in the graph corresponds
to one in. The reaction rate is the
change in the concentration of either
the reactant or the product over a
period of time. The concentration of
A decreases with time, while the
concentration of B increases with
time.

11. to determine the reaction rate of hydrolysis of aspirin, probably the
most commonly used drug in the world (more than 25,000,000 kg are
produced annually worldwide). Aspirin (acetylsalicylic acid) reacts with
water (such as water in body fluids) to give salicylic acid and acetic
acid,
Determining the Reaction Rate of Hydrolysis of Aspirin

12. Because salicylic acid is the actual substance that relieves pain and
reduces fever and inflammation, a great deal of research has focused
on understanding this reaction and the factors that affect its rate
Determining the Reaction Rate of Hydrolysis of Aspirin

13. Determining the Reaction Rate of Hydrolysis of Aspirin

14. Determining the Reaction Rate of Hydrolysis of Aspirin

15. Determining the Reaction Rate of Hydrolysis of Aspirin

16. Determining the Reaction Rate of Hydrolysis of Aspirin
The average reaction
rate for a given time
interval can be
calculated from the
concentrations of either
the reactant or one of
the products at the
beginning of the interval
(time = t0) and at the
end of the interval (t1).

17. Determining the Reaction Rate of Hydrolysis of Aspirin
The average reaction
rate for a given time
interval can be
calculated from the
concentrations of either
the reactant or one of
the products at the
beginning of the interval
(time = t0) and at the
end of the interval (t1).

18. Determining the Reaction Rate of Hydrolysis of Aspirin
Using salicylic acid, the reaction rate for the interval between t = 0
h and t = 2.0 h (recall that change is always calculated as final
minus initial) is calculated as follows:

19. Determining the Reaction Rate of Hydrolysis of Aspirin
The reaction rate can also be calculated from the concentrations of
aspirin at the beginning and the end of the same interval,
remembering to insert a negative sign, because its concentration
decreases:

20. Determining the Reaction Rate of Hydrolysis of Aspirin
If the reaction rate is calculated during the last interval given in (the
interval between 200 h and 300 h after the start of the reaction), the
reaction rate is significantly slower than it was during the first interval
(t = 0–2.0 h):

21. The Reaction Rate for a given chemical reaction is the measure of the
change in concentration of the reactants or the change in concentration
of the products per unit time.
The Definition of Reaction Rate

22. Rate = Δ [B]
Δt
=
Δ [A]
-
Δt
Molar concentration = brackets [A], [B]
Δ = “delta” change in
t = time interval

23. Sample Reaction Rate

24. Sample Reaction Rate
Given: balanced chemical equation and concentrations at specific times
Asked for: reaction rate
Strategy:
1.Using the equations subtract the initial concentration of a species
from its final concentration and substitute that value into the
equation for that species.

25. Solution
A Calculate the reaction rate in the interval between t1 = 240 s
and t2 = 600 s. , the reaction rate can be evaluated using any of three
expressions:
Sample Reaction Rate
2) Substitute the value for the time interval into the equation. Make sure
your units are consistent.
Subtracting the initial concentration from the final concentration of N2O5
and inserting the corresponding time interval into the rate expression for
N2O5,

26. Sample Reaction Rate
B Substituting actual values into the
expression

27. Sample Reaction Rate Boardwork

28. Sample Reaction Rate Boardwork
Answer:
9.0 × 10−6 M/s

29. Reaction Rate

30. Rate Law
The rate of a reaction is affected by the concentrations of
reactants. Rate laws or rate equations are mathematical
expressions that describe the relationship between the rate of a
chemical reaction and the concentration of its reactants.

31. Rate Law

32. Rate Law

33. Reaction Order
The reaction order is the relationship between the concentrations of
species and the rate of a reaction. The order of a rate law is the sum of
the exponents of its concentration terms.
whose experimental rate law is given by:
This reaction is third-order overall, first-order in A, second-
order in B, and zero-order in C.

34. Reaction Order

35. Reaction Order sample problem
1.Which of the following could represent the units of the rate reaction
that is 2nd order overall?
A) M s
2
-1
B) hr
1
C) M m
-1-1
D) M days
-1 -1

36. Reaction Order sample problem
1.Which of the following could represent the units of the rate reaction
that is 2nd order overall?
A) M s
2
-1
B) hr
1
C) M m
-2-1
D) M days
-1 -1
k : M x t
1-n -1
n=2
k : M x t
1-3 -1

37. Reaction Order sample problem
1.Which of the following could represent the units of the rate reaction
that is 2nd order overall?
A) M s
2
-1
B) hr
1
C) M m
-1-1
D) M days
-1 -1
k : M x t
1-n
-1
n=2
k : M x t
1-2
-1
the correct answer is
C

38. Reaction Order sample problem
2) Which of the following staight line plot correspond to a first order
reaction?
A) [A] vs t with a slope of -k
B) In[A] vs t with a slope of +k
C) 1/[A] vs t with a slope -k
D) In [A] vs t with a slop of -k

39. Reaction Order sample problem
2) Which of the following staight line plot correspond to a first order
reaction?
A) [A] vs t with a slope of -k
B) In[A] vs t with a slope of +k
C) 1/[A] vs t with a slope -k
D) In [A] vs t with a slope of -k
In [A] vs t : first order

40. Reaction Order sample problem
2) Which of the following staight line plot correspond to a first order
reaction?
A) [A] vs t with a slope of -k
B) In[A] vs t with a slope of +k
C) 1/[A] vs t with a slope -k
D) In [A] vs t with a slope of -k
In [A] vs t : first order
The correct answer is
D

41. Reaction Order sample problem
The initial concentration of reactants in a zero order reaction is 0.75 M. The
rate of a constant k is 0.015 M/min
Calculate the following
a) What will be the concentration of the reactant after 15 minutes
b) How long will it take the concentration t be reduced to 0.06M

42. Reaction Order sample problem
Solution
A) [A]f = -kt + [A]
[A]f = - 0.015 M/m x 15 mins + 0.75M

t=?
[A]= 0.75M
k= 0.015
M/min
[A]f= 0.06
(round off)

43. Reaction Order sample problem
Solution
A) [A]f = -kt + [A]
[A]f = - 0.015 M/m x 15 mins + 0.75M

t=?
[A]= 0.75M
k= 0.015
M/min
[A]f= 0.06
(round off)
= 0.525 M

44. Reaction Order sample problem
Solution
B) [A]f = -kt [A]0
0.06M = 0.015M(t) + 0.75
0.75 0.75
0.69M = 0.015M/min
-0.015 M/min
0.015M/min
t=?
[A]= 0.75M
k= 0.015 M/min
[A]f= 0.06

45. Reaction Order sample problem
Solution
B) [A]f = -kt [A]0
0.06M = 0.015M(t) + 0.75
0.75 0.75
0.69M = 0.015M/min
-0.015 M/min
0.015M/mint= 46 min
t=?
[A]= 0.75M
k= 0.015 M/min
[A]f= 0.06

48. -
3
-
1
-
1
What is the reaction order with respect to benzoyl peroxide?
What is the rate law for this reaction?
show the soluton