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Speed me up, Scotty!
by
Sally Lang
University
Grade: 10-12
Time Allotment:
Two fifty-minute class periods.
Subject Matter: Chemistry,
Mathematics, Computer Technology.
Overview:
In
chemical reactions, bonds are being broken and new bonds are being formed.
Whether or not a reaction proceeds depends upon the energy of the reactants
and the energy of the products. A reaction will proceed if the energy
of the products is lower than the energy of the reactants. In this case,
the reaction is said to be going "downhill". A reaction may proceed going
"uphill" if the products will achieve enough entropy (randomness) relative
to the products to overcome the increase in energy required for the reaction
to go. Even when the products of a reaction are at a lower energy than
the reactants (the reaction is "downhill") the reactants still must go
"up a small hill" before beginning its "big descent". This small increase
in energy required to begin a reaction is called its activation energy.
Since
chemical reactions are a consequence of atoms colliding with one another,
there are three main ways to increase the rate of a reaction. One way
is to increase the concentration of one of the reactants, increasing the
likelihood of atomic collision. Another way to speed up the rate of a
reaction is to heat the reactants, thus increasing the amount of collisions
likely to occur. This effectively lowers the activation energy. The last
way to increase the rate of a chemical reaction is to provide a catalyst,
a substance that serves to substantially lower the activation energy required
to get a reaction to proceed. This lesson explores the energy and entropy
changes in chemical reactions and the effects of concentration and catalysts
on the rate of reactions.
Learning Objectives:
Students will be able to:
- Describe the driving forces behind chemical
reactions.
- Define energy, entropy, exothermic reaction,
endothermic reaction, activation energy, and catalyst.
- Draw energy diagrams for "uphill", "downhill",
heated, and catalyzed reactions.
- List the three ways in which chemical reactions
can be accelerated.
- Design an appropriate laboratory experiment,
collect and analyze data, and draw conclusions.
- Employ Microsoft Excel to calculate and analyze
data and to create graphs and perform graphical analyses of that data.
Standards:
Taken from www.idahoachieves.com/standards.html
649. 01 Concepts of Scientific
Inquiry: Understand scientific inquiry and develop critical thinking skills
650. 02 Concepts of Physical Science: Understand the
structure and function of matter and molecules and their interactions.
650. 03. Understand chemical reactions
655. 01. Technology: Understand the relationship between
science and technology and develop the abilities of technological design
and application.
Media Components:
Video:
The Driving Force (The World of Chemistry) Program 13, Produced by the
University of Maryland and the Educational Film Center. Videocassette
Dist By 1990
Molecules in Action (The World of Chemistry) Program
14, Produced by the University of Maryland and the Educational Film Center.
Videocassette Dist By 1990
Web Sites:
http://members.aol.com/ChangChem3/CALbasicROR1.html
This web site explains the forces behind chemical reactions, The Collision
Theory of Atoms, factors affecting the rate of reactions, and real-world
examples of catalyzed reactions.
Materials:
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- 3 10-mL graduated cylinders
- 100-mL beaker
- stopwatch
- dropping pipet
- stirring rod
- apron
- safety goggles
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Prep For Teachers
Prior to teaching this lesson, bookmark the Web
Site on each computer in the classroom, and have the Video set to the
proper starting point. On the second day
of the lesson, when the laboratory will be performed by the students,
have all of the materials cleaned and set out at the laboratory stations.
Have at least 4 L of all three of the solutions
prepared. Have a copy of each of the attached
sheets available for each student.
Introductory Activities
Setting the Stage
Ask the students "Why do we keep certain foods in the refrigerator?" At
least one of your students will probably answer that the reason some food
is kept in the refrigerator is to keep if from going bad. Ask
your students, "What is happening to food when it goes bad?" You will
most likely get such answers as "it is breaking down", "it is rotting",
"it is a chemical reaction."
Ask the students how long they think it would
take some foods to break down and what would happen if it took their bodies
that long to break down food to use it for energy? Tell them that all
these questions deal with the rates of chemical reactions.
Pass out a Video Skeletal
Notes (Focus for Media Interaction) worksheet to each student, and
instruct them to complete it while watching the video segments. Begin
the Video, The Driving Forces. Focus for Media Interaction: While
watching the video Define -
Exothermic Reaction; Endothermic
Reaction and Entropy.
Start when you see the fire, just before the narrator
says, "In most chemical reactions, energy of the system decreases". PLAY
the video until you see the man in the lab coat with a bowl of lettuce.
FASTFORWARD until just after you see a wrecked building, just before
the man in the lab coat reappears. PLAY until you see wine glasses.
When you see the wine glasses, press STOP.
START the Video 14, Molecules in Action
at the beginning of the video. PLAY until after you see HBr formed
in animation and then STOP. Ask the students how they think increasing
the concentration of a reactant will affect the amount of collisions taking
place. Ask them how they think this will affect the rate at which HBr
will be formed. Press PLAY and continue the video. STOP
after you see the diagram showing that heat effectively lowers the activation
energy. FASTFORWARD until just before you see a big thumb and forefinger
removing a class stopper from some laboratory equipment. PLAY until
just after the next hill diagram. Then STOP. FASTFORWARD
until after you see a man holding in his hand a big ball and stick model
of a molecule. Before pressing PLAY, preface by telling the students
that they are in the middle of discussing a rhodium catalyst. Then press
PLAY. STOP after you hear "very little rhodium is lost."
To review the introductory part of the lesson,
ask the students what are the three things they learned that will cause
the rate of a reaction to increase.
Learning Activities
Distribute the Web
Site worksheet (FOCUS FOR MEDIA INTERACTION) to each of the
students. Explain to them that each student is required to complete one,
even though they will be working in groups of 4 or 5 on the computer.
Tell the students that when they have sufficiently
accessed the site for the provided URL, they need to click on the green
icon next to the word "Catalysts" under the Menu bar at the top of the
Web page. Release the students to their
computers to complete their assignment. Should take about 15 minutes.
When the class has reconvened, lead the
students in a 5 minutes discussion on their findings, asking the following
guiding questions.
- What did you discover to be the reason why
a catalyst speeds up a reaction? (After you receive their answers, explain
again that the catalyst merely forces the atoms in the proper position
to react, and that it does this by aligning them on its surface so that
they are right next to each other and can trade/share electrons.)
- What is the term for a biological catalyst?
(After they have answered, remind them of the question at the beginning
of class, and explain that it is because our bodies have enzymes that
we are able to break down food very quickly.
- Enzymes are put to use in several different
industries? What are some of those industries and how are enzymes utilized?
When the class is over, tell the students that
they will be performing reactions in the laboratory the following day
and that they will need to wear long pants and closed-toed shoes. Distribute
the laboratory sheets at this time and instruct students to read them
for homework so that they will understand the laboratory upon entering
the lab the next day.
Culminating Activity
Looking at the Procedure for the laboratory
(see attached), talk through the process with
the students following along. Ask them if there are any questions about
what they will be doing in the laboratory, and review any steps necessary.
Release the students into the laboratory.
Circulate the room during the experiment, answering any questions and
monitoring the students' safety. Allow 25-30 minutes for the students
to complete the laboratory.
When students have completed gathering data, have
them clean up their lab stations and return to the classroom.
Have the students go to a computer and following
the laboratory sheet instructions for Data Analysis, enter their data
and perform the necessary functions on the Microsoft Excel program. As
there will be 4-5 students at the computer in most classrooms, and not
all students will be able to be with their lab partner, each group of
4-5 at the computer should pick one set of data to work from. (All data
should be within the same ballpark, and exhibiting the same trends, anyway.)
If you are lucky enough to have access to as many computers as you have
lab groups, you should require each lab group to do their own Excel data
analysis. Each student should turn in a laboratory sheet, but only one
Excel Workbook and Graph are required per computer group.
At the end of class, review the class on their
findings with the following questions:
- Do your graphs look as you expected them to?
Why or why not?
- What do you think a T vs. time graph would
look like? (falling from left to right).
- How much effect did the catalyst have on the
rate of the reaction?
Extensions
English-Students write a detailed laboratory
report including conclusion and sources of error.
Math-Students calculate the concentrations
of the solutions by hand instead of relying on the Excel program.
Math-Students study the rate of change
of chemical reactions using rudimentary differential calculus (if applicable
for that grade level)
Health-Students make a flow chart demonstrating
the specific enzymes required to break down food during the digestive process.
Community Connections:
- Take a fieldtrip to your local dairy farm,
cheese factory, or brewery. What enzymes are used in these processes?
Under what conditions must the reactions take place to keep the enzyme
active? Write a report or prepare a PowerPoint presentation about the
industry you chose and its reliance on enzymes.
- Visit a cement company. Find out the amount
of time required for cement to form up. What would be some of the consequences
of not allowing it enough time? What would be some of the consequences
if the cement hardened to quickly? Why are the cement drums on the trucks
always spinning? Write a report about the Chemistry behind cement.
- Go to your local library and research enzymes
in the body. Consult a physician. How many enzymes are in the human
body? What are some examples of diseases that occur as a result of a
person lacking that enzyme? While there are too many to list, prepare
a report of a disease about which you learned. Consult a physician or
the Internet, and provide examples of symptoms and prognoses.
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