Download The Initiation of Thermodynamic Theory from the Particulate Model

TEACHING THERMODYNAMIC USING THE PARTICULATE MODEL
OF MATTER
Ma-Naim Chana
Kibbutzim College of Education, Tel-Aviv, Israel.
[email protected]
Bar Varda
Science Teaching Center, Hebrew University, Jerusalem, Israel
Finkental Michael
Rachah Institute of Physics, Hebrew University, Jerusalem, Israel
ABSTRACT
Traditional teaching of thermodynamics still leaves many misconceptions amongst
students and teachers. In this study, with pre service and in service teachers we used
a different approach of teaching thermodynamics: teaching started from the particulate
model of matter. Concepts and phenomena concerning heat and temperature changes
were explained through the processes that occur among particles. It was hypothesized
that using this model facilitates the assimilation of the formal scientific concepts of
thermodynamics by making them more visual and concrete. In the following article, we
will explain the teaching method that was employed.
INTRODUCTION
Research on concept development reveals difficulties with basic concepts of
thermodynamics. For example, difficulty in differentiating between “heat”, an extensive
parameter, and temperature-an intensive parameter; students identify certain materials
as “hot” and others as “cold”. These typical misconceptions were found among students
and among varied groups of adults even after being exposed to a course in
thermodynamics. A survey of textbooks at different levels shows that most present
“heat” and “temperature” through macroscopic phenomena, using them later to present
the concept of internal energy. The microscopic explanation usually appears as an after
thought.
In the following study we conducted an experiment where the teaching sequence was
changed. We did not follow the historic sequence where formal thermodynamics
concepts were introduced before the “modern” particulate model of matter as defined
towards the end of the 19th century. Instead, we presented extensively the particulate
model of matter first, thus definitions of concepts of thermodynamics like heat,
temperature and internal energy were based on the model. Less elaborate explanations
based on the notions of the particulate model of matter were given even before
Newton’s time.
Explanations based on the particulate model of matter were preferred since it is a
mechanical model that appeals to common sense. We believe these explanations make
more sense to students than explanations based on the formal thermodynamic
concepts. Macroscopic phenomena which students encounter, can all be explained by
using the particulate model of matter.
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Phenomena were discussed and explained on three levels:
1. Description of the macroscopic phenomena;
2. Explanation of the process through the particulate model of matter;
3. Statement of energy changes that occurred in the system.
THEORETICAL BACKGROUND
This study follows the traditional studies of conceptual development, (Driver, 1985;
Novak, 1977), which have the following common assumptions:
1.
Every person, regardless of age, holds a system of explanations for natural
phenomena and definitions of scientific concepts.
2.
These explanations based on everyday experience and common sense are
usually different from the scientific ones.
3.
Understanding and applying new knowledge are influenced by the former
system of definitions and explanations.
4.
Alternative concepts are resistant to change.
These assumptions have been supported since then by a vast body of research (Pfundt
& Duit, 1994). Studies based on the traditional sequence of teaching where macro
descriptions come before the microscopic model, report that students show difficulties in
understanding phenomena concerning heat. These difficulties were found among
elementary school students, university students and university researchers (Linn &
Songer, 1991).

Differentiating between heat (mass dependent) as an extensive parameter, and
temperature (mass independent) as an intensive parameter. Stavy & Berkovitz
(1980) reported wrong answers given to questions of mixing water at different
temperatures. Many of the students think that the temperature of the mixed quantity
is the sum of the temperatures of the ingredients. The confusion between heat and
temperature was also exposed by Shayer & Wylam, (1981); Wiser &Cary, (1984);
Finley, (1985); Linn & Songer, (1991). Rozier & Viennot (1991) found this confusion
among teachers and university students, as well.
 Accepting the fact that all inanimate objects in a room have the same temperature in
spite of the fact that metals feel “cold” while plastic or wood feel “tepid”. This difficulty
derives from the different feeling while touching objects and from identifying
objects/materials as associated with typically “hot” (wool for example) or typically
“cold” (metals or aluminum foil). This characterization of materials influences
students’ alternative explanations concerning which material is needed in order to
keep hot or cold body temperature constant. Certain materials are assumed to keep
“heat” (keeping a comparatively high body temperature) and other materials keep
“cold” (keeping a comparatively low body temperature). Thus, in order to keep the
body temperature, it should be covered with the appropriate material.
 A dichotomized concept of hot and cold fighting each other was observed by
Tiberghien (1985); Tomasini, & Balandi (1987); Lewis & Linn (1994).
 Heat is thought to be something contained in a body, something (“matter”) that flows
from a hot body to a colder one (Finley 1985): “Heat is something in the body that
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changes the temperature and velocity of its particles.” This is a crude conception of
the classical caloric.
 A hot/cold body is made of hot/cold particles (Finley 1985), when one side of a body
is heated, “hot molecules move from that side to the other”, namely, students apply
macroscopic characteristic to a microscopic quantity.
These findings strengthen an assumption that one has to start with the particulate model
of matter; to specify first what is happening in the microscopic level, the macroscopic
phenomena then become clear.
METHODOLOGY
Description of the new curricula unit
One. A thorough instruction of the particulate model of matter preceded the instruction
of temperature and “heat”
Two. Within this unit the words “heating” and “cooling” were consistently used instead of
the notion quantity of “heat”.
Three. All the macroscopic phenomena were explained on 3 levels: description of the
process using the particulate model of matter; the changes of energy involved in
those processes; a detailed description of the macro changes manifested during the
observation of the phenomena and experiments.
Four. Three forms of energy were specifically defined and used consistently: Kinetic
Energy, Potential Energy and Radiation Energy.
Kinetic Energy – the energy the particles have due to their motion, it is mass dependent
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and the amount of this energy is given by the formula E k  mv 2 .
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Potential Energy – is the energy the particles have due to the state they are located in
a substance. The potential energy is actually the sum of the bond energy between the
molecules. The bond energy is lower when the distance between the molecules is
small and higher when the distance between the molecules is greater. We can
compare the bond energy to a spring’s potential energy, when the spring is extended
(similar to longer distances between molecules) the potential energy is higher. The
internal energy of a system is defined as the sum of the Kinetic Energy of and
Potential Energy of its particles.
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Examples of issues treated in the unit
Heating a block of ice
A thermometer is inserted in a block of ice contained in a metal box. The box is laid over
a Bunsen burner. Looking at the thermometer, we see an increase of temperature until
the reading is 0 0C. At this point, the temperature remains constant for some time and
the ice melts. When all the ice has melted, the temperature starts to increase again and
some steam comes out. The temperature increases till the reading is 100 0C. At this
point, an increase in steam emitted is observed and there is no change of temperature.
From the energy point of view, we say that there is a change in the internal energy of the
ice, a change that occurs because we heat the ice.
From the particulate model of matter aspect, we should discuss the following issues:
 What happens to the particles while heating (in the solid, liquid and gaseous
phases)?
Heating changes both the kinetic energy of particles and the potential energy of the
particles in the solid. The increase in the potential energy causes an increase of
distance between the molecules. The increase of kinetic energy of particles causes
increase of temperature.
 Why is there a period of time with no change of temperature when the
thermometer reading is 0 0C or 100 0C?
The change of temperature is observed until the distances between some particles are
at the distances typical of the liquid state of matter. From this point, the change in
internal energy is only due to a change in the potential energy. There is no change in
kinetic energy, therefore there is no change in temperature. When the bonds between
the particles weaken, a phase change is observed. Further heating causes changes in
both the potential and the kinetic energy. The same happens in boiling. All the energy
given to the liquid through heating leads only to a change in the potential energy. There
is only a change in the potential energy of matter at 1000C, a change that causes the
molecules to separate and, thus, the liquid changes into gas. There is no change in the
kinetic energy, therefore, there is no temperature change. This change in potential
energy is what is called “latent heat” a name that was given in the 17th century.
 Why does steam come out of the liquid even before boiling?
The temperature of matter depends on the average kinetic energy of its particles.
Among the particles, some have high kinetic energy while some have low kinetic energy.
If a particle with a high kinetic energy is on the surface of the liquid, there is a possibility
that it will be ejected from the liquid. These particles are the ones that form the steam
that comes out of heated liquid, even before the boiling temperature.
 Why does the phase change liquid–gas, need a longer period of heating than the
phase change solid-liquid?
The change in distances between molecules from solid to liquid is very small while in the
phase change of liquid-gas we have to break the inter-molecular interactions and
separate the molecules. Therefore, this phase change needs a greater amount of
energy and a longer heating period.

What is there in the bubbles that rise from the bottom of the liquid?
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The bubbles consisting of liquid or vapor are at a temperature higher than the
temperature of the surrounding liquid. These bubbles rise due to buoyant force.
Mixing liquids in different temperatures
A plastic container comprises of two compartments of equal volume, separated by an
insulated partition. Water at a temperature of 10oC is poured into one compartment and
water at a temperature of 600C is poured into the other compartment. The partition is
then removed and the water from the two compartments is mixed together.
In the discussion that follows, we describe the exchange of kinetic energy between
colliding molecules. Molecules with high kinetic energy (from the high temperature liquid)
collide with molecules with low kinetic energy (from the low temperature liquid). After
some time all the molecules of the liquid will have the same mean kinetic energy. In the
case of equal quantities of the same liquid the final mean kinetic energy of the molecules
is
PURPLE
the average of the kinetic energy of the components.
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Temperature measuring
In the language of the particulate model of matter, the collisions between the substance
molecules and the thermometer molecules is changing the kinetic energy of both. After a
while the “temperature” is the same. The description involves the change of temperature
of the thermometer components from the outer glass cover to the liquid in the inner
narrow tube. From this discussion two question rise:
1.
How do we know that the thermometer is really measuring the temperature and
gives the correct system temperature?
2.
How can we be sure that the thermometer is not changing the system’s
temperature?
From our experience it is usually the first time the students deal with measuring
instruments the way the are designed and the principle of their operation. A detailed
discussion using the particulate model of matter follows.
In every process in every question, qualitative as well as quantitative, we ask the student
to give the scientific story from the three points of view we mentioned above:
macroscopic; the particulate model of matter; energy changes. We stress the fact that
this story is not the story of a single molecule or a single particle but the story of a
cluster of a great number of particles, almost an infinite number. The teaching follows
the model of Mastery Learning, where understanding and utilizing the model is more
important than covering the whole unit.
SUMMARY AND CONCLUSION
The main assumption of this study, that the particulate model of matter should be well
known and correctly applied by the learners before approaching the topic of “heat”, was
supported both by observing the quantitative results of the pre/post tests and by
analyzing the qualitative explanations. Explanations were clear, concrete and not
declarative as we found in the control group. For instance in the case of cooling due to
water evaporation the control group used the explanation “water have a tendency to
cool”. The experiment group explained that some of the particles with high kinetic energy
escaped leaving behind molecules with lower mean kinetic energy.
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students: What are appropriate cognitive demands? Journal of Research in
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