Peer-Led Team Learning Orientation Workshop
January 24, 2002
City College of New York

Exercise
The basic postulates of Dalton’s theory are as follows:[1]

1. Each element is composed of extremely small particles called atoms.

2. All atoms of a given element are identical.

3. Atoms of different elements have different properties (including different masses).

4. Atoms of an element are not changed into different types of atoms by chemical reactions; atoms are neither created nor destroyed in chemical reactions.

5. Compounds are formed when atoms of more than one element combine.

6. In a given compound, the relative number and kind of atoms are constant.

Activity:

Each person in the group takes one of the postulates above, and using beans (red, black, white), makes an explanatory image on the tabletop. Use the following elements in your work:

Oxygen      =         red
Carbon       =         black
Hydrogen   =         white
and the combustion of methane with oxygen to form water and carbon dioxide as the chemical reaction.

Write a chemical equation for this reaction.
Each person in turn will explain her/his point to the group, to illustrate that point.
How are the two laws of chemical combination (Law of conservation of matter and the law of multiple proportions) explained by Dalton’s theory?

Instructor/Facilitator Questions:

Debrief all groups, and have the responses scribed on newsprint (have experienced students scribe):

1. How was each postulate illustrated?

2. Was this easy or hard? What was easy or hard about doing this exercise? What actions or behaviors were exhibited by group members?

3. What techniques were used? (Name)

4. What words needed to be defined?

5. Did the group ask questions of the leader?

6. Did the leader ask questions of the group?

7. Would this be useful for teaching Introductory Chemistry? Why or why not?

8. Who was John Dalton?

[1] Postulates are from Brown, T.L., LeMay, H.E., Bursten, B.E. (1991). Chemistry: The Central Science (5^th Ed.). Englewood Cliffs, NJ: Prentice Hall. Page 34.

PLTL sessions open up multiple dimensions in exploring learning materials. One that is particularly suitable for workshops is what can be termed the kinesthetic or haptic dimension, utilizing physical models that involve the sense of touch and that are visual. These examples are not normally accessible through computer animation, which precludes three-dimensional touch. Such models lend themselves to small group exploration, and in the process of manipulating the models, students can obtain an intuitive understanding and feeling for the constraints, interactions, and dynamics of systems that are in many cases difficult, even for experts, to intuit from equations or visual representations alone. The use of physical models has played a significant role in scientific thought and discovery (see Sept 6, 1999, C&EN, “Tetrahedral Carbon Redux,” by A. Maureen Rouhi.)

In groups of three to eight, use a “Round Robin” technique, passing the scorekeeping to Person C, with Persons A & B passing pennies. The first person is A, the second is B, the third is C for the first step; for the second step, “B” becomes “A”, “C” becomes “B”, and the next person becomes “C.”

1. Consider a simple chemical reaction, A®B, that follows a first-order rate law, rate = k [A]. You will model this reaction with pennies. Start with 100 pennies, which will represent the initial concentration of A, 100 mM. Each penny will therefore represent 1 mM.

Student A (SA) will represent the concentration of A, and Student B (SB) will represent the concentration of B. We will represent the reaction of A to form B by passing pennies from SA to SB. Each exchange of pennies will represent one second of time. Student C will ask each student for the observed results and record it.

We will model a reaction in which 10% of the concentration of A reacts per second. Thus for each exchange (each second), SA should transfer 10% of his/her pennies to SB. Round fractions to the nearest penny. Continue this exchange for 15 seconds. Record concentrations of A and B (number of pennies) each second (after each exchange step) in the table below.

Time (s)	[A] (mM)	[B] (mM)
0	100	0
1	90	10
2	81	19
3
4
5
6
7
8
9
10
11
12
13
14
15

Plot the concentration of A versus time on the graph below. Use a different color to plot the concentration of B versus
time on the same graph.

2. Let’s apply the modeling technique developed in Question #1 to a reversible reaction, A<=>B.

In each second (exchange step), allow 10% of A to react to form B, and allow 10% of B to react to form A. Record the results in the first two columns of table below.

	10%	10%
Time (s)	[A] (mM)	[B] (mM)
0	100	0
1	90	10
2	82	18
3
4
5
6
7
8
9
10
11
12
13
14
15

Plot the concentration of A versus time for the 10%/10% reaction on the graph below. Compare this graph to the irreversible reaction A®B, in Question #1.

3. Consider the reversible case, A<=>B , in each second ( exchange step), allow 10% of A to react form B, and allow 5% of B to react to form A. Predict the position of equilibrium (i.e. the equilibrium number of pennies). Will A or B be greater? Perform the simulation with pennies to confirm your prediction.

Exercise
The basic postulates of Dalton’s theory are as follows:[1]

Purpose

Introduction:

Follow-up Exercise:

	Dalton's Postulates (word document download)
	The Kinetics Problem (word document download)
	The S-mores Problem (word document download)

Exercise The basic postulates of Dalton’s theory are as follows:[1]

Purpose

Introduction:

Follow-up Exercise:

Exercise
The basic postulates of Dalton’s theory are as follows:[1]