Transcript Chemical Kinetics Lab 2 Purpose This lab will help you explore the meaning of the term chemical kinetics. You will be able to use.

Chemical Kinetics
Lab 2
Purpose
This lab will help you explore the meaning of the term
chemical kinetics.
You will be able to use this knowledge to evaluate the
rate law for one reactant from graphical relationships
generated from the changing concentration of the
reactant over time.
Reaction(s)
5 SO32-(aq) + 2 IO3-(aq) + 2 H+(aq) →
I2(aq) + 5 SO42-(aq) + H2O(aq)
starch(aq) + I2(aq) → starch I2· complex
Kinetics
• Explores the steps by which a reaction
takes place
• The main step by which a reaction takes
place is described by a rate law of the
rate-limiting step of the reaction.
• The rate is studied only under forward
conditions and is determined by the
number of effective collisions and the
energy per collision.
Reactions and Rates
• Effective collisions must occur with the
correct orientation of species and
sufficient energy
• The reaction could be facilitated or
inhibited by molecular / ionic structure.
• The rate of a reaction is affected by these
things (among others):
o Temperature
o Concentration
o Presence or absence of a catalyst
Procedure
1. Determine the reaction order of the reaction
with respect to the iodate ion
•
•
Find the reaction times of six solutions by varying the [IO3-],
but holding the [SO32-] constant.
Determine the reaction order by finding the linear plot.
2. Determine the reaction order of the reaction
with respect to the sulfite ion. (Beyond the
scope of this class.)
3. Combine rate laws to determine the overall
reaction order and rate law. (Beyond the
scope of this class.)
Concentration Decay Curve
The shape (and function) of this curve depends on the order of the
reaction.
[X], M vs. Time, s
0.008
0.007 T0
[IO3-], M
0.006
T1
T2
0.005
0.004
T3
0.003
T4
T5
0.002
0.001
T6
0
0
100
200
300
Time, s
400
500
Reaction Plots
• To determine which reaction order a reaction
follows, and therefore, which rate law a reaction
obeys, we plot three different graph types for
each reagent participating in the reaction.
• Whichever graph yields a linear response
dictates the reaction order and rate law to be
used.
Zero Order Reaction
[X], M
[X], M vs. Time, s
0.600
0.500
0.400
0.300
0.200
0.100
0.000
y = -0.0100 x + 0.500
R² = 1
0.0
20.0
40.0
60.0
Time, s
• Linear when [x], M vs. Time, s is plotted.
• k = -m; In this case k = 0.0100 What should the unit be?
•Rate Law: Rate = k[x]0 = k; In this case Rate = 0.0100
First Order Reaction
ln [X]
ln [X] vs. Time, s
2.500
1.500
0.500
-0.500 0.0
-1.500
-2.500
-3.500
y = - 0.0332 x - 0.560
R² = 0.9987
10.0
20.0
30.0
40.0
50.0
60.0
Time, s
• Linear when ln [X] vs. Time, s is plotted
• k = -m; In this case k = 0.0332 What should the unit be?
• Rate Law: Rate = k[X]1= k[X] ; In this case Rate = 0.0332[X]
Second Order Reaction
• Linear when 1/[X], 1/M vs. Time, s is plotted.
• k = m; In this case k = 0.0225 What should the unit be?
• Rate Law: Rate = k[X]2; In this case Rate = 0.0225[X]2
1/[x], 1/M
1/[X], 1/M vs. Time, s
y = 0.0225 x + 1.89
R² = 0.9996
12.00
10.00
8.00
6.00
4.00
2.00
0.00
0.0
100.0
200.0
Time, s
300.0
400.0
Rate Laws
• A rate law is a mathematical description of a
reaction rate’s dependence on concentration.
• When you identify the rate law for your reaction, be
sure to substitute in a value for k and an identity for
the X in [X].
Safety Concerns
• Reagents:
o
o
o
o
o
Potassium Iodate (0.1 N)
Potassium Sulfate
Sodium Sulfite
Soluble Starch
Sulfuric acid (0.1 N)
• Eye Contact:
o Irritation, redness, burns, pain, and irreversible damage.
• Skin Contact:
o Irritation, redness, burns and pain.
• Inhalation:
o Coughing, sneezing, sore throat, labored breathing, burns, delayed lung
edema and chest pain.
• Ingestion:
o Nausea, vomiting, diarrhea, gastric irritation, circulatory disturbances, and
CNS depression
Precautions and Waste
• All solutions are acidic and must be disposed
in the acid waste container in the fume hood.
• Iodine stains clothing and skin! Be careful
when working with your solutions today. Wear
gloves if you’d like to protect your hands.
Lab 3 Reminder
• Read through the write-up for Lab 3.
• Complete the pre-lab questions for Lab 3
and submit them by the deadline.
• Complete and submit your Lab 2 Report at
the start of next week’s lab.
• Study for the quiz.