Unformatted text preview: the halflife of a first order reaction is known, the
When
rate constant can easily be calculated with the above
equation or vice verse. Half Life of First Order
Half Integrated Rate Law
Integrated Second Order Reactions: A → Products Rate = k[A]2
Rate A + B → Products
Rate = k[A][B] For one substance ∆[ A ]
Rate = ∆t 1
1
= kt
[A]t [A]0 Integrated Rate Laws
Integrated Second Order Reactions 1
1
= kt
[A]t [A]0 Halflife for 2nd Order 1
t1 =
k [ A] 0
2 Halflife for Second Order Reactions
Halflife Zero Order Reactions
Zero They do not depend on the
They
concentration of any reactant.
concentration A products t t 0 0 ∫ ∆[ A] = ∫ k∆t Rate = k ∆[ A ]
Rate = ∆t ∆[ A ]
k=∆t [A]t  [A]0 = kt Zero Order Reactions
Zero Integrated Rate Law [A]t  [A]0 = kt Halflife expression [A]0
t1/2 =
2k Integrated Rate Laws
Integrated Zero Order reactions [A]t  [A]0 = kt First Order reactions [A ]
ln
[ A] t = kt 0 Second Order reactions 1
1
= kt
[A]t [A]0 Integrated Rate Laws The hydrolysis of sucrose in water to glucose and fructose
The
is a first order reaction at 25 C. It takes 3.33 hours for the
[sucrose] to drop from 1.20 M to 0.60 M. How many hours
are required for the [ ] to change from 0.800 M to 0.0500
M? might need halflife equation
M? A) 0.90 hr b) 1.33 hr c) 13 3 hr d) 5.63 hr Integrated Rate Laws
Integrated Iodine atoms combine to form molecular iodine in the gas phase. I(g) + I(g) → I2(g) This reaction follows secondorder kinetics with k = 7.0 x
10–1 M–1s–1 at 23°C. (a) If the initial concentration of I was 0.086 M,
10–1
calculate the concentration after 2.0 min. A) 3.83x1036 M b) 2.85 M (b) Calculate the halflife of the reaction if the initial concentration of I
(b)
is 0.60 M and if it is 0.42 M.
is c) 0.010 M d) 0.076 M Determination of Rate Law
by the Graph Method
by Rate Data For
2 NO2 → 2 NO + O2
Time (hrs.)
0
30
60 Partial
Pressure NO2,
Pressure mmHg
mmHg
100.0
62.5
45.5 ln(PNO2) 1/(PNO2) 4.605
4.135
3.817 0.01000
0.01600
0.02200 90
120
150
180 35.7
29.4
25.0
21.7 3.576
3.381
3.219
3.079 0.02800
0.03400
0.04000
0.04600 210
240 19.2
17.2 2.957
2.847 0.05200
0.05800 37
37 Rate Data Graphs For
Rate
2 NO2 → 2 NO + O2
Partial Pressure NO2, mmHg vs. Time
100.0
90.0 Pressure, (mmHg) 80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
0 50 100 150
Time, (hr) 200 250 Rate Data Graphs For
Rate
2 NO2 → 2 NO + O2
ln(P NO2) vs. Time
4.8
4.6
4.4
4.2
ln(pressure) 4
3.8
3.6
3.4
3.2
3
2.8
2.6
2.4
0 50 100 150
Time (hr) 200 250 Rate Data Graphs For
Rate
2 NO2 → 2 NO + O2
1/(P NO2) vs Time
0.07000
0.06000 Inverse Pressure, (mmHg 1 ) 1/PNO2 = 0.0002(time) + 0.01 0.05000
0.04000
0.03000
0.02000
0.01000
0.00000
0 50 100 150
Time, (hr) 200 250 Reaction Mechanism
Reaction Is a sequence of molecular events, or steps, that
Is
defines the path by which reactants become
products.
products. The single steps in a mechanism are called
The
elementary steps (reactions).
elementary The sum of the elementary steps results in the
The
overall reactio...
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 Fall '08
 STAFF
 Reaction, Kinetics, Rate equation, Rate Law Expressions

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