1

Reaction Rates

On July 20, 1944, a one-armed and one-eyed man broke a vial of acid and let the contents begin

reacting with copper wire. In thirty minutes the wire would be severed, a massive chemical explosion

would result, and Adolf Hitler would be assassinated. Colonel Claus Von Stauffenberg had just started

an unstoppable chemical reaction that he believed

would changed the course of history.

The rate of this chemical reaction had been

carefully measured. Stauffenberg placed the

bomb in a briefcase and calmly walked into the

meeting room in the Wolfs Lair (Wolfschanze),

where Hitler was in a meeting with the military

leaders of the Third Reich. Inside the case, the

acid was silently reacting with the copper wire.*

A few minutes before the reaction of this fuse

was complete Stauffenberg slipped out, confident

that they would all be dead within minutes.

Stauffenberg should have stayed in the room.

Moments before the wire was severed, the case was casually moved by one of the men, placing it right

behind a large oak leg of the desk.

At 12:40 P.M. the bomb detonated, and 975 grams of plastic explosive exploded with a massive force,

killing many of the people in the room. Because of the last-minute shifting of the case, Hitler was

injured but not seriously, and survived until April 30, 1945, when he took his own life. Before he did,

Claus Von Stauffenberg was arrested, tortured, and executed. His final words were “Long live our

sacred Germany!”

In this unit we will be investigating the rate of chemical reactions, similar to the reaction used as a

fuse to detonate the bomb in the attempted assassination just described. Our goal is to determine

how these rates can be measured, and to study the energetics of these reactions.

The most important skill to be learned in this unit is to be able to perform a chemical reaction and

report how fast the reaction is going. To do this you will observe and perform several reactions and

determine the reaction rates in various units. You will be able to quantitatively find out:

-How fast does nitric acid react with copper wire (this was the fuse for the bomb described

above)

-How fast does magnesium react with hydrochloric acid?

-How fast do things such as methanol, ethanol, and gasoline burn?

*If time allows your instructor may demonstrate this chemical reaction using various inorganic acids and metal

wires.

How can we find out how fast a chemical reaction goes?

Colonel Claus Von Stauffenberg (left) as portrayed

by Tom Cruise (right) in the Movie Valkyrie (2008).

2

3

4

5 ways to change the rate of reaction

• Hit it with a STICC!

• Change the

• 1. Surface area

• 2. Temperature

• 3. Identity (of reactants)

• 4. Concentration (of reactants)

• 5. Catalyst

4

5

6

Labs and Worksheets

7

Name: ______________________________________ Period: _____ lab13.1

Factors Affecting Reaction Rates

Introduction:

Chemical reactions occur at different rates. The combustion of methane is a relatively fast reaction,

while the rusting of iron is quite slow. In general we would like to make the rusting of iron proceed as

slowly as possible. On the other hand, an explosives chemical company might want to speed up the

reactions that produce the explosives they sell. In order to understand how the rates of chemical

reaction can be controlled, it is necessary to understand the collision theory of chemical reactions.

A chemical reaction involves bond breaking and bond forming. The states that,

in order to react, molecules must collide with each other with sufficient

force and the correct positioning to break old bonds and form new ones. The minimum energy that

the colliding molecules must have for the reaction to occur is called the activation energy. According

to the collision theory, any factor that increases the number of molecular collisions that occur, or

that increases the amount of energy with which the molecules collide, will increase the rate of the

reaction.

In this experiment, you will study the effect of temperature, concentration of reactants, particle size and surface area on the rates of chemical reactions. You will also investigate the effect that

catalysts have on reaction rates. Catalysts are substances that provide a path of lower activation

energy for reactions without being consumed.

Objective: To observe the effects of temperature, concentration, particle size, surface area and

catalysts on the rates of chemical reactions.

Pre-lab questions:

1. Predict the effect of temperature, concentration, and particle size on the rate of a

reaction.

3. An enzyme is an example of a catalyst: a substance that increases the rate of a chemical

reaction without being consumed. Based on the collision theory, draw a picture of a how an

enzyme might work.

collision theory

8

Station One: The effect of temperature on reaction rate.

1. You have available magnesium, 6M HCl, ice water, and hot water. In one sentence describe your

experiment.

2. Make a table of your data and carefully graph your results.

3. Write a balanced chemical equation for the reaction between hydrochloric

acid and Magnesium. (Hint: It is a single replacement reaction, and Mg forms a

+2 cation

4. Describe in your own words the effect of temperature on the rate of a reaction.

5. Explain this effect in terms of the collision theory.

Station Two: The effect of reactant concentration on reaction rate.

6. You have available magnesium, and HCl of various concentrations. In one sentence describe your

experiment.

7. Make a table of your data and carefully graph your results.

8. Describe in your own words the effect of concentration on the rate of a reaction.

9. Explain this effect in terms of the collision theory.

9

Station Three: The effect of surface area on reaction rate.

10. You have available several metals of various shapes and sizes, a mortar and pestle, a pair of

scissors, and hot plate capable of magnetic stirring. Note that stirring a solution will effectively

increase the surface area of the reactants. In one sentence describe your experiment.

11. Tabulate your data and graph your results:

12. Write a balanced chemical equation for the reaction between hydrochloric

acid and aluminum. (Hint: It is a single replacement reaction, and Al forms a +3 cation

13. Describe in your own words the effect of surface area on the rate of a reaction.

14. Explain this effect in terms of the collision theory.

Station Four: The effect of a catalyst on reaction rate.

You have available a computer with access to the internet. Provide examples of three chemical

reactions whose rate of reaction may be increased by the use of a catalyst. Do not attach any

printouts.

15. Inorganic chemical reaction

Write a balanced chemical equation:

Catalyst(s):

16. Organic chemical reaction

Write a balanced chemical equation:

Catalyst(s):

17. Biological chemical reaction

Describe this reaction, or write a balanced chemical equation:

Catalyst(s):

18. Describe in your own words the effect of a catalyst on the rate of a reaction.

19. Explain this effect in terms of the collision theory.

10

Conclusions:

20. Of the various methods for increasing the rate of reaction, which do you believe can have the

greatest effect and why?

21. You may have observed non-linear graphs. Explain this observation.

11

12

Name_____________________________Period________________________ Lab 13.2

Plastic Milk: A Reaction rate investigation

Introduction: Milk is Arrhenius base, meaning that it has a pH >7 due to hydroxide (OH-) ions. When

reacted with the mild acid in vinegar (acetic acid), The milk separates into curds, whey and casein.

The casein is a polymeric protein (plastic) that separates to the bottom.

Your tasks:

1. Develop a procedure that will create this plastic as rapidly as can be safely done. This may involve

some trial and error. It may be useful to recall the 5 parameters that can increase the rate of a

reaction:

1.________________. 2.________________. 3.________________. 4.________________.

5.________________.

2. Once your final procedure is developed, write an experimental procedure. Remember, a usable

written procedure is one that can be repeated by anyone.

3. Once your plastic is isolated, you may mold it into any tasteful object you like.

The following materials are available; you don’t have to use them all.

Skim milk

1% milk

Regular milk

Red vinegar

White vinegar

Food coloring (for fun)

1M HCl

Cloth and elastics for filtering

Suggested procedure:

Try mixing about 100 mL of milk with 10 mL of vinegar for starters.

1. Here is our original planned procedure. Be sure it is repeatable

2. To improve the speed of making this polymer, optimize 2 variables.

Variable tested: Result

1.

2.

13

3. Based on this, here is our detailed final listed procedure.

4. Questions:

A. Of the parameters you tested, which made the biggest difference and why?

During this investigation, have someone go online to answer:

B. What is casein?

C. Write below the chemical structure of casein.

14

15

Name: ______________________________________ Period: _____ ws13.1

Reaction Rates

Directions: For each of the following questions use the appropriate relationship or equation to solve

the problem.

1.

2.

3.

16

4. Given the following data for the decomposition of hydrogen peroxide (H2O2), calculate the rate of

reaction in moles H2O2 consumed per liter per minute for each time interval.

Initial concentration of H2O2: 3M

Concentration of H2O2 after 3 minutes: 1.3M

5.

6.

17

Name: ______________________________________ Period: _____ ws13.2

Reaction Rates Practice Quiz

Work in pairs and see how well you do on this practice quiz.

Directions: For each of the following questions use the appropriate relationship or equation to solve

the problem.

1. In the reaction of hydrogen and oxygen to create water, the concentration of hydrogen changes

from 2 M at time = 0 to 0.2 M at time = 2 seconds. What is the reaction rate for this consumption of

hydrogen?

2. List three ways to increase the rate of a chemical reaction.

3. Given the following data for the decomposition of hydrogen peroxide (H2O2), calculate the rate of

reaction in moles H2O2 consumed per liter per minute for each time interval.

Initial concentration of H2O2: 2.6 M

Concentration of H2O2 after 3 minutes: 1.53 M

18

Questions 4-5 refer to the energy diagram above

4. For the energy diagram above, what single element is being transferred in the chemical reaction of

carbon monoxide with nitrogen dioxide to form carbon dioxide and nitrogen monoxide?

5. Is the reaction above endothermic or exothermic?

Questions 6-9 refer to the energy diagram above

6. Which number refers to products?

7. Which number refers to activation energy?

19

8. Which number refers to the transition state, at which point the starting material and product form

an activated complex?

9. Show the distance on the graph that represents the overall energy change for the reaction and

indicate whether this reaction is endothermic or exothermic overall.

10. For the reaction:

2AlCl3 2Al + 3Cl2

The rate of loss of AlCl3 is 3 mol/L sec. Therefore the rate of formation of aluminum metal is

also_______, and the rate of formation of Cl2 is ________.

Extra credit (1 point): Do the rates observed in question number 2 make sense, knowing that one mole

of HCl reacts with one mole of Cl2 to form 2 moles of HCl? Explain.

20

21

How to Ace the Reaction Rates Test howtoaceitunit13

In this unit we considered an important property of a chemical reaction: the rate at which it

proceeds. We observed how concentration can affect the rate of a reaction, and came up with four

other possible methods as well: temperature, surface area, the inherent reactivity of the reactants,

and catalysts. All can greatly influence the rate of a reaction.

We discussed ways to measure the rate of a reaction at any given point in time. This is easy enough,

since the rate of a reaction is equal to the change in concentration over time. The concentration

of the reactants will decrease, and products increase as a reaction proceeds. The units for

concentration are mol/L, and bracketed chemicals indicate concentration; for example [HCl] literally

means “the concentration of Hydrochloric Acid”.

We also looked briefly at the collision theory of a chemical reaction in order to understand the rate

and energetics involved. Molecules must collide with enough force and at the right location on the

molecule to form products. The moment where the new bonds are forming, and the old bonds are

breaking is called the transition state, and that intermediate chemical is called the activated complex.

This led to a discussion of the energy change in a chemical reaction, since forming the activated

complex always involves adding energy to the system. That amount of energy is called the activation

energy. Overall the reaction may be exothermic or endothermic, easily recognizable by comparing the

energy state of the products compared to the reactants. These can easily be seen by looking at a

reaction energy diagram.

Once a reaction rate has been determined for a substance it is easy to find the rates for all other

reactants involved, since it is proportional to the coefficients in the balanced reaction.

In many cases chemists are not concerned what the rate of a reaction is, unless it is inconveniently

slow or explosively fast. In our next unit we will see how the equilibrium of a reaction can prevent a

lot of reaction from being isolated, and that usually bugs them. This topic (equilibrium) is coming up

next.

To ace this unit you should review this entire packet, including lab experiments, powerpoint

presentations, and worksheets. You should also be familiar with the information below:

1. Know the following terms:

A. reactant

B. product

C. transition state

D. activated complex

22

E. exothermic

F. endothermic

G. Activation energy

Be able to determine

2. What is necessary for a chemical reaction to proceed (collision theory)

3. 5 ways to change the rate of a reaction

4. Given an energy diagram, be able to determine:

How much energy a reaction, or the reverse reaction, needs to proceed

5. Where the transition state is

6.How exothermic or endothermic a reaction is

7. Rate of reaction given reaction time and concentration change

• Example:

• [HCl] at time = 0: 0.22 M

• Start reaction

• [HCl] after four seconds 0.32 M

• What is the reaction rate?

8. In the energy unit we learned how to predict if a reaction will take place spontaneously. In this unit

we determined how to measure how fast a reaction is. What is the relationship, if any, between

reaction rate and spontaneity? To consider this, answer each question with a brief explanation

- are fast reactions always spontaneous?

- if the free energy of a reaction is highly positive, is it a slow reaction?

-Are fast or spontaneous reactions dangerous

-Are fast reactions exothermic?

23