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1. Science notes
· Λ'::·"··-rr.
mass dropped, by making the same series of
measurements and calculations with the 16 gram
steel ball provided with the PASCO free-fall adapter.
Almost the same results were obtained (Figure 3).
The graphs of height id) as a function of time
squared (t
2
) for both masses are almost identical
(Figures 4 and 5) as are the graphs of the acceleration
due to gravity (g) as a function of height (d) (Figure
6). In both cases, this indicates a slight influence of
air friction as height increases.
Sources
Pasco Scientific, PO Box 619011, 10101 Foothills
Boulevard, Roseville, CA, USA (www.pasco.com)
Logal products distributed in the UK by TAG Developments
Ltd, 25 Pelham Road, Gravesend, Kent DAI 1 OHU, and by
CAPEDIA Ltd, Harford Centre, Hall Road, Norwich NR4
6DG (www.logal.com)
References
Kluk, E. and Lopez, J. (1992) Don't use air-tracks to measure
gravity acceleration. The Physics Teacher, 30, 48.
Ramirez, S. and Ham, J. (1990) Systematic errors in an air-
track experiment. The Physics Teacher, 28, 602.
Rueckner, W. and Titcomb, P. (1987) An accurate
determination of the acceleration of gravity for lecture hall
demonstration. The American Journal of Physics, 55, 324.
Schoch, F. and Winiger, W. (1991) How to measure g easily
with -10"
4
precision in the beginners' lab. The Physics
Teacher, 29, 98.
Ricardo Trumper is a Senior Lecturer in the Department of Mathematics and Physics, Faculty of Science and
Science Education, Haifa University, Israel. E-mail: rtrumper@research.haifa.ac.il
Moshe Gelbman was, from 1993 up to 1998, a physics teachers' instructor in the Tomorrow 98' project based
at the Hebrew University, Jerusalem. He now develops microcomputer-based physics practicals for high schools.
Chemkin: new software for studying chemical kinetics
Pavlos Mihas and George Papageorgiou
Chemical kinetics is a significant area in chemistry,
but a difficult one for teaching and learning. Since
the usefulness of software as a teaching and learning
tool has been realised, a number of programs about
□netics have been developed. Many involve spread-
sheet applications (e.g. Brosnan, 1992), the MS-DOS
environment (e.g. Ramette, 1993), or multimedia (e.g.
Russell and Kozma, 1994).
This note introduces a new program, Chemkin,
designed to help learners clarify aspects of chemical
kinetics, providing interactivity, realistic data and
results, multiple representations of the results and a
wide range of applications and parameters.
Basic characteristics of the software
The software has been developed using Visual Basic
5.0. It runs in the Windows environment (version 95
or higher).
Among the advantages of the software are the
following:
II It is simple to get started in it, although it provides
the user with many options.
1 00 School Science Review, June 2001, 82(301)
□ It leads the user step by step through the processes.
The multiple representations make the results
more comprehensible.
□ Its scientific accuracy is very satisfying for high
school students.
□ No extra software or hardware is needed.
Figure 1 shows a screen shot of the software in use.
The software enables the user to study two main
areas: chemical reactions and radioactive decays
(including radioactive series).
As far as chemical reactions are concerned, the
user can study transformations of a substance A into
a second B, or even into a third C, any of which can
be reversible or not (according to the user's prefer-
ence).
For example, one can study the transformations:
A B → C
Apart from the type (reversible or not) and the number
of steps in the reaction, the parameters that the user
can define for the chemical reactions are: temperature;
concentration of the initial reactant A; the rate constant
k of each step.

2. >
With regard to radioactive decays, the user can
study transformations of atoms of an element A into
a second B, a third C or even a fourth D (non-
reversible), according to the user's preference.
For example, one can study the radioactive series:
A→ Β —> C — D
Apart from the number of steps, the parameters that
can be defined for the radioactive decays are:
temperature; initial number of atoms of the element
A; the decay constant k of each decay.
Users can design their own reaction (or decay) or
study a pre-set example. Additionally, they can study
statistical aspects of the reaction, make optimisations
or study the change of reaction rate versus time. For
simplicity, all transformations (including chemical
reactions and certainly radioactive decays) follow the
rate law of the first-order reactions.
How and where the software could be used
The software could be a useful tool for studying
aspects of kinetics with students as it takes into
Science notes
consideration pedagogical issues. It can be used in
the final years of high school, in the^eontext of a
computer-assisted learning approach.
Using the software, chemical reactions or radio-
active decays are studied as transformations among
A, B, C, etc. and are represented through simple
schematic representations such as:
A —> Β, A —) Β —> C, A ^ Β —> C, etc.
and not by the exact equations. For example, when
the substance N2Os(g) is transformed into N02(g), the
equation of the reaction is:
2N2 05 (g)-»4N02 (g) + 02(g)
A schematic representation of this transformation is:
N2O5->NO 2
Furthermore, the software can be used for the study
of the effects of changes in some of the parameters
described above on the process of a chemical
reaction(s) or a radioactive decay series designed by
the teacher or the student, and also on the formation
of the final products. Only a few seconds are required
Graphs
·.
Ιιυυ,υυ
Figure 1 A screen shot of the Chemkin software.
School Science Review, June 2001, 82(301) 101

3. ·
:
to change the values of the parametersand repeat the
process. Compare the results of .eachcase, students
can draw their conclusions. They can slso see that
the radioactivee decays are not reversible and that
temperature has no effect on the process.
The software can also help students with
understanding chemical equilibrium. They can study,
for example.the reactions A —>Β and A BThey
can easily change the rate constants of any direction
(k; k-1
) orthetemperature,and. comparing the results,
rihrgr can draw their conclusions. Students can also
see that Κ = k/k-1
. As a result, students can acquire a
cfcarer view of the meaning and importance of the
constantskinthewholeprocessand the formation of
the final products.
The statistical considerations can also be studied
effectively by using the software. For example, how
does die number of atoms (or moles) affecttheresults?
What does the optimisation do? Students can
appreciate the fact that increasing the number of atoms
makes the fluctuations in the graph (Figure 1) above
and below the optimised curve (which corresponds
ιo.:averylarge number of atoms) become less extreme.
£1 tfee case of the chemical equilibrium, when the
r—Ter of atoms is small, the fluctuations (either in
the graph or in the bars) are larger, emphasising the
tyTi^rniz character of the equilibrium. Representation
:ofparticies with spots (Figure 1) canalsohelp students
to sce the random character of the reactions (or
the decays)
the software) the kinetics of first-order reactions. This
gives the opportunity to an instructor to explain what
the order of a reaction is and also that radioactive
decays follow, in general, the rate law ofcfirst-order
chemical reactions.
The software can help students to clarify what the
rate constant k (or the decay constant k) means. In a
simple reaction A Β they canreplace concentration
ofA by 1 mol/1 (in a decay they can replace number
of atoms Ν by 1). Changing k, students can see what
is changed in the process of the reaction (or decay).
Additionally, students can study more realistic
cases with the software, by using a pre-set example.
Thus, the study of carbonic acid (for the chemical
reactions) shows that, in this case, the concentration
could also affect the values of the rate constant k, due
to the fact that pH changes when the concentration of
the acid changes.
The software is available upon request from the
first author via e-mail: pmichas@eled.duth.gr.
References
Brosnan, T. (1992) Probabilistic modelling of chemical
equilibrium. School Science Review, 74(266), 92-94
Ramette, R. W. (1993) KinWorks: A learning tool for kinetics
lab. Journal of Chemical Education Software, SP 6B2.
Russell, J. W. and Kozma, R. B. (1994)
4M:CHEM-Multimedia and mental models in chemistry.
Journal of Chemical Education, 71, 669-670,
The whole study can help students to understand
Aspectsofthe mechanisms of chemical reactions, and
That the transformations among A, Β and C follow (in
Pavlos Mihas is an Assistant Professor of Physics, and George Papageorgiou is an Associate Professor of
Chemiestry, in the Department of Primary Education, Democritus University of Thrace, Alexandroupolis 68100,
©neece.
-02 School Science Review, June 2001, 82(301)