Chemical Kinetics - Mr. Robinson's General Chemistry Pages
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Transcript Chemical Kinetics - Mr. Robinson's General Chemistry Pages
Chemical Kinetics
The Study of Reaction Rates
What is a Rate?
β’ The rate of a process in the amount of
progress that has been made, divided by the
time required to achieve that progress.
β’ Speed =
βπππ π‘ππππ
βπ‘πππ
β’ Example: You travel 102 miles in 2.00 hours
β’ Average Speed =
102 ππ
2.00 βπ
=
ππ
51.0
βπ
The Rate of a Chemical Reaction
β’ In a chemical reaction, we can define
βprogressβ as the consumption of a reactant
or the formation of a product.
β’ To measure this progress, we measure how
much a reactant concentration decreases in a
given period of time, or how much a product
concentration increases in a given period of
time.
The Rate of a Chemical Reaction
β’ But not everything in a chemical reaction is
changing at the same rate.
β’ 2A(g) + 3B(g) ο C(g) + 4D(g)
β’ Suppose the concentration of substance A is
decreasing at the rate of 0.40 mol/ L s. What
is happening to the other concentrations?
The Rate of a Chemical Reaction
β’ 2A(g) + 3B(g) ο C(g) + 4D(g)
β’
β’
β’
β’
β[π΄]
πππ
= -0.40
βπ‘
πΏπ
β[π΅]
πππ
= -0.60
βπ‘
πΏπ
β[πΆ]
πππ
= 0.20
βπ‘
πΏπ
β[π·]
πππ
= 0.80
βπ‘
πΏπ
Standardizing the Rate of a Chemical
Reaction
β’ 2A(g) + 3B(g) ο C(g) + 4D(g)
β’ Rate = -
β[π΄]
2βπ‘
= -
β[π΅]
3βπ‘
=
β[πΆ]
βπ‘
=
β[π·]
4βπ‘
β’ All of the above expressions give the same
result.
β’ β’ -
1
2
1
3
πππ
πππ
(β0.40
) = 0.20
πΏπ
πΏπ
πππ
πππ
(-0.60
) = 0.20
πΏπ
πΏπ
Standardizing the Rate of a Chemical
Reaction
β’ 2A(g) + 3B(g) ο C(g) + 4D(g)
β’ Rate
β’ Rate
β’ Rate
β[π΄]
β[π΅]
β[πΆ]
= = =
2βπ‘
3βπ‘
βπ‘
πππ
= 0.20
πΏπ
1
πππ
πππ
= (0.80
) = 0.20
4
πΏπ
πΏπ
=
β[π·]
4βπ‘
Reaction Rate from Concentration
Measurements
TIME (Seconds)
[H2O2]
0
0.882
60
0.697
120
0.566
180
0.458
240
0.372
300
0.298
360
0.236
420
0.188
480
0.152
540
0.120
600
0.094