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Course Syllabus Chemistry I/II Ions and Common Substances Nomenclature Competency Sheet Examination I Objectives: Thermochemistry Activation Energy Problem Set Periodic Table
04/18/23
Requirements
• Laboratory• Chem 201/202 Laboratory Manual
“An Introduction to Experimental Chemistry” (Bookstore)
• Safety Goggles (Voucher from Bookstore)• Quadrille ruled bound laboratory notebook• Pen• Proper Attire
04/18/23
Course Syllabus
• Course grade depends on• Three Exams• Final Exam• Competency tests and quizzes• Problem Sets / Assignments• Laboratory Notebook & Reports
04/18/23
Activation Energy
Reading assignment:• Chang: Chapter 15.4
This lecture continues a discussion of the factors that affect the rate of a chemical reaction.
The topic of activation energy is introduced along with the Arrhenius equation.
Reaction Rate
- dPA
dt= k [A]
n
Factors that affect the rate of reaction
concentrationor pressure
catalyst
particle sizetemperature
Reaction Coordinate DiagramCollision Theory
Ene
rgy
Reactants Products
Ea
H
For a chemical reactionto occur, the reactantsmust collide successfullywith enough energyto overcome theactivation energy (Ea).
If the products aremore stable than the
reactants, H < 0, the reaction is exothermic.
04/18/23
Ene
rgy
Reactants Products
Reaction Coordinate DiagramCatalyst
Why does therate of reaction
change when a catalystis added?
Why does H for thereaction stay the same?
04/18/23
Arrhenius EquationFactors Affecting the Rate of Reaction
k = A e-Ea/RT
Rate constant
Geometric factor Activation energy
Temperaturedependence
(kelvin)
Rewrite the Arrhenius equation in straight line form.
The Arrhenius equation allows the rate of a reactionto be calculated at different temperatures.
Arrhenius Equation
The rate constant for a chemical reaction is4.0 x 10-4 s-1 at 280. K
and2.0 x 10-3 s-1 at 300. K.
What is the activation energy of this reaction?
What rate constant would be expected at 320. K?
k Temp(K) ln kInverse Temp K
0.00040 280 -7.82 0.003570.0020 300 -6.21 0.00333
-6760 16.318
lnk320 -4.806k320 0.0082
Activation Energy Determination
y = -6759.6x + 16.318
R2 = 1
-8.00
-7.00
-6.00
0.00320 0.00340 0.00360
Inverse Temp (1/K)
ln k
Boltzmann Distribution
energy
num
ber
of m
olec
ules
T2 > T1
average
The rate of many organic chemical reactions doublewith every 10 degree change in temperature.
Reaction Rates vary with Temperature
If you run a fever of a 103 °F,how much “faster” is your body running,
than at a normal temperature?
The rate of many organic chemical reactions doubleswith every 10 degree Celcius change in temperature
around room temperature.
k Temp(K) ln kInverse Temp K
0.00040 280 -7.82 0.003570.0020 300 -6.21 0.00333
-6760 16.318
lnk320 -4.806k320 0.0082
Activation Energy Determination
y = -6759.6x + 16.318
R2 = 1
-8.00
-7.00
-6.00
0.00320 0.00340 0.00360
Inverse Temp (1/K)
ln k
k Temp(K) ln kInverse Temp K
0.00040 280 -7.82 0.003570.0020 300 -6.21 0.00333
-6760 16.318
lnk320 -4.806k320 0.0082
Activation Energy Determination
y = -6759.6x + 16.318
R2 = 1
-8.00
-7.00
-6.00
0.00320 0.00340 0.00360
Inverse Temp (1/K)
ln k
Temp(oC)Time(s) Temp(K) InvTempK k lnk9.5 106 282.6 0.003539 59.4 4.08
14.4 73 287.5 0.003478 86.3 4.4619.9 45 293 0.003413 140.0 4.94
25.1 30 298.2 0.003353 210.0 5.35 -6644 27.593130.2 22 303.3 0.003297 286.4 5.66 173.51 0.59291
0.998 0.033361466.1 3Formaldehye-Bisulfite Activation
Energy Determination
y = -6643.7x + 27.593
R2 = 0.998
4.00
4.50
5.00
5.50
6.00
0.0032 0.0033 0.0034 0.0035 0.0036
Inverse Temp (1/K)
ln k