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Students are often taught standard methods for solving equilibrium problems—methods
that they then apply to solving similar problems on homework assignments,
quizzes, or exams. When asked questions designed to ascertain whether they
understand what actually occurs in an equilibrium system, the same students
often answer incorrectly. What seem to us small modifications in a problem
often cause students to have great difficulty solving the problem. Thus it
is generally accepted (1) that students who score well on examinations do
not necessarily understand the fundamental concepts of chemical equilibrium.
Screen from Equilibrium showing an initial
system and an equilibrated system.
The
general chemistry textbook is not the problem with teaching and learning
chemical equilibrium. Textbooks usually contain good written descriptions
of the topic with instructive accompanying figures; the equilibrium table
approach in most textbooks is also useful. However, textbooks are often ineffective
at helping students visualize a concept well enough so that they can make
predictions and apply concepts.
The goal of the applet described here is to
help students visualize some aspects of chemical equilibrium. We began by
compiling a list of different
aspects of chemical equilibrium that we thought could be taught effectively
using a visual approach. Based on this information, we programmed this applet
that allows students to add colored balls to a reaction chamber. Each ball
represents 0.5 moles of N2, H2, or NH3. Clicking the “Equilibrate” button
displays the equilibrium concentrations of each gas in a chamber that is
next to the initial chamber. Thus, students can see how many of each colored
ball are present initially and after equilibrium concentrations have been
reached. Students can vary the starting concentrations of any of the gases.
They can also change the value of the equilibrium constant by changing the
temperature of the system. The initial and equilibrium concentrations of
each gas are given in an equilibrium table. The value of “X” that
would be obtained by solving the equilibrium constant expression is also
listed.
The applet can be used by the instructor in the classroom as the topics
are introduced and by students for individual study. Sample exercises for
students
are included. The text is available in English and Spanish.
Literature Cited
- Nurrenbern, S. C.; Pickering, M. J. Chem. Educ. 1987, 64, 508–510.
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