By: Anne, Krishna, Trinh, Tao, Manjot, & Sergey

Activation Energy

Intro: The Importance

Knowledge of the activation energy and arrhenius equation for a reaction

allows us to change variables to increase the

rate at which products are formed.

Activation Energy with Phosphorushttp://www.youtube.com/watch?v=9rR6OEQRFZQ&feature=fvwrel

Intro: What is Activation Energy?• Activation energy (Ea):

"the minimum amount of energy (in kj/mole) that must be absorbed by a system to cause it to react"

• Important factors:• Temperature-an increase

helps the rxn reach the transition state

• Orientation-the reactants have to collide in a certain orientation to react

Chemistry and Chemical Reactivity

Purdue Chemed Reaction Coordinate Diagramhttp://chemed.chem.purdue.edu/genchem/topicreview/bp/ch22/

activate.html

Intro: What did we learn?

Arrhenius Equation: relates temperature (T), orientation (Z) and the rate constant (K) of the reaction to the activation energy.

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch22/activate.html#rate

Temperature rule of thumb: every 10 C increase double in the rate of the reaction

Set Up/ Procedure

Safety• ALWAYS wear goggles, gloves, & lab

coat at ALL times during the experiment• Long hair must be tied back.• Wear close toed shoes.

CAUTION• If you get any chemical on your hands or

clothes, wash affected area thoroughly with water for 15 mins.

• Notify instructor immediately.

Materials• 1- 10 ml graduated cylinder• Small beakers• Small & large test tubes• 1 stop watch• volumetric pipets• 1 thermometer• 10 ml of 0.0100M KI• 10 ml of 0.00100M Na2S203

• 10 ml of 0.0400M KBrO3 • 10 ml of 0.100M HCl• 1 ml of 0.5% starch

Set Up• Use small beakers & estimate volumes from the

markings on the beakers when getting reagents. DO NOT WASTE REAGENTS.

• Bring reagents to work area in clean, labeled appropriate containers.

Cont. Set Up• Put 50 ml of DI water in a beaker.• Use 1 graduated cylinder and 1 transfer pipet

for EACH REAGENT. – Make sure they are clean and dry to start. If not,

rinse the graduated cylinder and pipet with a small amt. of reagent

• LABEL EVERYTHING.

General Mixing Information• You will run the reaction 4 times at

diff. temperatures.• For each run, have the following

ready: • Test tube #1 : Large test tube

Place 2.0 ml of KI, 2.0 ml of Na2S2O3 & 2.0 ml of H2O

• Test tube #2 : Small test tube Place 2.0 ml of KBrO3, 2.0 ml of HCl,

and 3 to 4 drops of starch solution

Reaction Run # 1 (Room temp)• Pour the contents of test tube # 2 into test

tube # 1

Reaction Run # 2 (10°C)• Slowly swirl test tube # 1 and test tube # 2 separately for approximately 5 minutes in a 250 mL beaker of water at a temperature of about 10°C.

Reaction Run # 3 (30°C)• Repeat the experiment at about 30°C, warming all reactants in a 250 mL beaker to that temperature before starting the reaction.

Reaction Run # 4 (40°C)• Repeat the experiment at about 40°C, warming all reactants in a 250 mL beaker to that temperature before starting the reaction.

result?

The rate of reaction roughly doubles for every 10°C rise in temperature . Higher temperature, faster reaction.

10 15 20 25 30 35 40 450

0.0000001

0.0000002

0.0000003

0.0000004

0.0000005

0.0000006

0.0000007

0.0000008

0.0000009

0.000001

2.78000000000001E-07

0.000000139

0.000000505

0.000000951

Reaction Rate & Temperature

Temperature

Reac

tion

Rate

11.8 C

21.5 C

29.4 C

39.8 C

What is the Results?

Why is that ?

• Because of increasing collision frequency, and kinetic energy of particles; therefore, particles can overcome the activation energy to react.

0.0031 0.0032 0.0033 0.0034 0.0035 0.00360

1

2

3

4

5

6

f(x) = − 6048.84667571235 x + 24.3035142469471R² = 0.99917587373372

Activation Energy

1/T

lnk

Ln k 3.77 3.08 4.37 5.001/T 0.00339 0.00351 0.00330 0.00319

The Arrhenius Plot

y = mx + b

m=-Ea/R

E= 5.0 x 10^4 (J/mol)

Conclusion• Did the results match your hypotheses?• Arrhenius Equation is supported by our

experiment

Conclusion

Conclusion• Sources of Error?• How can we improve the lab?

Learning Experiences!• In this experiment we learned that before any

reaction can start, molecules of the reactants have to bump or collide into each other. This collision must be strong enough to cause the reactants to smash into each other with a certain amount of energy or the reaction will not occur.

• To form new bonds in the product, old bonds must break in the reactants, and breaking bonds takes energy. To start any chemical reaction, a minimum amount of energy is needed. This is also known as the Activation Energy!

• That’s exactly why we use the “The Arrhenius equation” k = Ae-Ea/RT , it gives the relationship between the temperature, T, and the rate constant, k. A is a constant proportional to the collision frequency. Ea is the activation energy, the minimum energy required for a successful molecular collision.

Real World?

• One example of a reaction that needs energy to start is the burning of gasoline. You have probably seen movies in which a car plunges over a cliff, lands on the rocks below, and suddenly bursts into flames. But if some gasoline is spilled accidentally while filling a gas tank, it probably will evaporate harmlessly in a short time.

Well… It Happens In the Movies?• Why doesn’t this spilled

gasoline explode as it does in the movies? The reason is that gasoline needs energy to start burning. That is why there are signs at filling stations warning you not to smoke. Other signs advise you to turn off the ignition, not to use mobile phones, and not to reenter the car until fueling is complete. This is similar to the lighting of the Olympic Cauldron as you will witness the next slide.

• No Activation Energy = No Explosion.

Did You Know?• Another great example of

activation energy are the Cauldrons that are designed for each Olympics. Each cauldron contain highly flammable materials that cannot be extinguished by high winds or rain. However, they do not ignite until the opening ceremonies when a runner lights the cauldron using a flame that was kindled in Olympia, Greece, the site of the original Olympic Games.

Let’s Review!

Let’s Review a little bit more..Hint… You MIGHT have to participate in the next slide

• The Arrhenius equation, k = Ae-Ea/RT , gives the relationship between the temperature, T, and the rate constant, k. A is a constant proportional to the collision frequency. Ea is the activation energy, the minimum energy required for a successful molecular collision.

Obviously We Learned Something, But Did You?

• Lets Try One:A second-order reaction was observed. The reaction rate constant at 276K was found to be 8.9 x 10-3 L/mol and 7.1 x 10-2 L/mol at 308K. What is the activation energy of this reaction?

Activation energy is the amount of energy required to initiate a chemical reaction. The activation energy can be determined from reaction rate constants at different temperatures by the equation.

Solution• Find The Activation Energy.

THE END

Lab Handout – Exp. E: Activation Energy Kotz, John C., Paul Treichel, and John Raymond. Townsend. Chemistry &

Chemical Reactivity. 7th Edition. Australia: Brooks/Cole, 2010. Print "The Activation Energy of Chemical Reactions." The Activation Energy of

Chemical Reactions. Web. 14 July 2012. <http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch22/activate.html >.

YouTube.com. Web. 14 July 2012 <Activation Energy with Phosphorus<http://www.youtube.com/watch?v=9rR6OEQRFZQ&feature=fvwrel>

"Dnatube Scientific Videos." DnaTube.com.Web. 16 July 2012. <http://www.dnatube.com/video/4887/Activation-energy >

"Activation Energy Problems ~ Analytical Chemistry." Activation Energy Problems ~ Analytical Chemistry. Web. 16 July 2012. <http://www.analyticalchemistrygsu.com/2012/02/activation-energy-problems.html>

<http://chem.chem.rochester.edu/~chm132tr/worksheets/workshop_08_activation.pdf >

All pictures: Microsoft Office Clip Art - < http://office.microsoft.com/en-us/images/results.aspx?&ex=2&qu=chemistry>

Works Cited/ References