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Transcript
Developing Energy Conception of Students in Chemistry Class:
Research on the learning and teaching of energy by BNU Group
Wang Lei Wang Weizhen Wei Rui Jing Zhiying Jiang Tao Meng Qingrui
Chemistry College of Beijing Normal University
[email protected]
Introduction
In the framework for K-12 science education, energy, one of the core ideas, is also discussed
as a crosscutting concept. Besides the definitions of energy at both the macroscopic and
microscopic scales, energy transfer and conservation, as well as the relationship between energy
and forces are focused on as the main questions in energy learning.
In chemistry education, besides matter, energy is another major theme in chemistry learning.
Energy is a word that is used so much in school that there are many misconceptions about it.
Students consider energy as a concept related to life, health and food (Black &Solomon, 1983).
Not only primary school students, but also some high school students still think energy is
immeasurable (Solomon, 1985; Watt, 1983). Researchers found that when students say energy is
conserved, they mean energy is stored in a system, and can be released in an initial form (Brook&
Driver, 1984; Kesidou & Duit, 1993; Solomon, 1985). Survey research also shows that
endothermic reactions are not thought to be spontaneous, and that students consider outside
conditions on a spontaneous judgment basis, like heating, rather than Gibbs free energy (Gabriela,
Ribeiro, Pereira Ma, 1990; Boo, 1998). Teachers also lack an overall understanding of energy and
how to teach important ideas about energy. Although they are familiar with the content, the
importance of teaching energy, and what is the most difficult for students to learn, teachers need to
more information covering many aspects regarding the teaching of energy.
Based on research literature on the learning and teaching of energy, we focus on the
following questions: Is energy teachable and learnable for various students? What energy ideas
should be taught at the various grade levels? How do we teach energy concepts? In the first part of
the paper, we introduce the general framework of our research, including the content about energy
in the high school science curriculum of Mainland China, and considerations about the basic
structure of students’ epistemic systems. Then, we review research from our group research the
teaching and learning about energy. We conclude this paper by discussing implications of our
research.
General framework
1. The content about energy in the high school chemistry curriculum
Energy is major component of the high school’s chemistry curriculum. Much of the
curriculum focuses on reactions and energy with less attention to the relationship between the
structure of substance and its properties and energy. In Mainland China, from the curriculum
reform in 2001, building the energy conception in chemistry learning has become a focus of
reform. In high school, students learn knowledge about energy presented in Table.1. The
curriculum includes the following ideas: the energy in reactions, atomic structure and chemical
bonding, thermochemistry, and electrochemistry.
1
Table.1 Items about energy of high school curriculum standard in Mainland China
Theme
Items in high school curriculum standard
Junior High School
Chemical change:
basic characteristics
Chemistry & social
development:
chemistry & energy
1.
Know about energy change in chemical reactions,
2.
Realize the importance of gaining energy from reactions.
1.
Know the importance of complete combustion,
2.
Describe the influence to the environment when using fuels like hydrogen, biogas,
utilization
petroleum gas, alcohol, gasoline and coal, identify the least pollution fuel.
3.
Explain the significance of fossil fuel,
4.
Know the rich resources in sea.
Senior High School- compulsory stage
Chemistry reactions
& energy
1.Use chemical bonding to explain the reason of energy change in reactions
2.Describe the examples of transformation between chemical energy and thermal energy
in daily live.
3.State the transformation between chemical energy and electric energy and application
in life by giving an example.
4.Identify the importance of raising combustion efficiency, developing clean energy, and
new fuel cells.
Junior High School- selective stage
Module theme: Material structure & properties
Atom structure &
1. Identify ionization energy and electronegativity,
Element properties
2. Use ionization energy to explain the element properties.
Chemical bonding&
material properties
3.
1.
Know extra nuclear electrons transition and the application.
Know the application of lattice energy, and use the value to predict the strength of
ionic bond.
Module theme: Chemical reaction principle
1. Explain the energy changes in reactions and transformations in energy states.
Chemistry reactions
2. Collect information to explain how energy is important to humans, including
& energy
describing the significance of chemistry in solving fuel problems.
3. State the transformation between chemical energy and thermal energy,
4. Explain heat of reactions, Enthalpy change, and calculate energy changes using
Hess’ law.
5. Use an inquiry process to understand the transformation between chemical energy
and electric energy,
a. Explain the principle of cells,
b. Write equation of electrode reactions and cell reactions.
c. Collect information online to know categories and principles of
electrochemical cells,
d. Evaluate the application of the transformation between chemical and
electric energy.
6. Explain metal corrosion and investigate preventive measures.
2
Reaction rate &
chemical equilibrium
1.
2.
3.
4.
2.Identify activation energy and its influence on reaction rate.
Predict the direction of reaction through the value of enthalpy change and entropy
change.
Describe the process of chemical equilibrium and apply K to calculate conversion
ratio
Conduct an inquiry to determine the influence of temperature, concentration, and
pressure to chemical equilibrium,and explain the result.
In Mainland China, energy has received more attention since the curriculum reform. The
change can be seen not only from the number of items in the curriculum standards, but in the
energy themes that are covered. In selective stages of senior high school, the section in Table 1
named “Chemistry reactions & energy”, which includes the knowledge of thermochemistry and
electrochemistry, is organized according to the energy conversion (transformation), for example
between chemical energy and heat energy, and between chemical energy and electric energy .
However, because there are not so obvious energy clues in other parts of standard chemistry
curriculum, the energy view is sometimes ignored in teaching. Another problem is the knowledge
of energy is still valued more than the ability to analyze issues from an energy perspective.
Chemistry focuses only on some of the ideas in energy construct. In chemistry, energy is
discussed mainly in two dimensions (Figure 1).
Figure 1. Two dimensions of energy in high school chemistry
First, what is energy? It can be explained both at the macro- and microscopic levels, but in
senior high school, the emphasis is on the microscopic (See Figure 2).
Figure 2. What energy ideas are discussed in chemistry
3
An atom is the smallest indivisible particle of matter. It is the basis of matter and reactions.
The energy inside an atom is the total energy related to chemical reactions. But the energy inside
atomic nucleus (nuclear energy) is just involved in nuclear reactions, which is different from
chemical reactions. As a result, the energy outside the atomic nucleus is the one discussed in
chemistry. We don’t mean that the kinetic and potential energy just belongs to the atomic nucleus
and electrons themselves. All of this constitutes total energy of an atom, which with the energy of
other atoms, as well as attraction potential energy caused by nuclear attraction and repulsive
potential caused by repulsive force from other electrons, constitute total energy of a polyatomic
molecule and make up the energy of matter.
Second is energy transfer and transformation. The transformation between chemical energy
and thermal energy (heat energy), also chemical energy and electric energy are the focal point of
energy learning in high school.
2. The epistemic model of energy
Energy conception is an overall understanding of energy. It is not only learning knowledge, but
building the energy epistemic model. We believe that there is an interior factor which influences
specific concept learning and a student’s cognition about specific topics. The factor is a kind of
thinking model or perspective which is used in conceptual understanding and problem solving. We
call it an “epistemic model”. We recognize that it is related with “epistemic field” based on
specific field of subject, and there are three core construction elements as “epistemic perspective”,
“epistemic path” and “ thinking style ”. We found that there are strong relationships between the
progression of epistemic model and the learning of core concept (knowledge).
To raise a theoretical model, we focus on two questions in our research: (1) what knowledge and
core concepts are the key points of learning to build the epistemic model. (2) How many kinds of
epistemic results (performances) occur, and what are they? In response, we built a theoretical
epistemic model of energy, which consist of four parts: epistemic field, epistemic perspective,
epistemic category (thinking style), and epistemic results (performance). Epistemic field is the
4
chemistry content we focus on. The wide-depth of the field is changeable. For instance, when we
put emphasis on the whole of energy, it is an epistemic field, and we could study it as a whole to
figure out corresponding perspectives and category of thinking style. But when we narrow down
the range of study, we may consider energy transformation of the reaction system as an epistemic
field. In a certain epistemic field, the relationship of epistemic perspectives, category of thinking
style and results (performance) can be seen from Figure 3.
Figure 3. In a specific epistemic field, the structure of epistemic model
Epistemic results are the external performance. Some verbs like describe/explain/predict/design
usually are used to show different levels of students epistemic performance. Epistemic
perspectives are the internal basic cause of the results and performance, and are different with
different cognition content and epistemic fields. Epistemic style categories are generally classified
with macroscopic or microscopic, qualitative or quantitative, unsystematic or systematic, and
stable or dynamic. Combined with the above epistemic factors is a description of the learning
progression level students reach in certain fields. For example, Figure 4 shows us the ideal
(expected) epistemic model when students face the epistemic field of “the factors which influence
energy change of a system’’. “Reaction heat” and “△H of system” are the first level of epistemic
perspectives. We can also identify them as the sub-epistemic field of “the factors which influence
energy change of a system”. Macroscopic and microscopic reasons of a system are epistemic
perspectives. When students use chemical bonds to examine the concept, this indicates reaching a
microscopic level of learning. We also use verbs like describe/explain/design to show different
levels of epistemic results and performance. Different epistemic perspectives lead to an epistemic
category differential and various epistemic results. In order for students to build a conception of
energy, the key point of research is to find out what are the epistemic perspectives behind multiple
performances. These perspectives are the focal points in teaching and learning. The model is also a
framework for evaluating textbooks and designing attainment tests.
Under this general framework, we carried out the research on energy teaching and learning.
Our research aim is to find out the epistemic perspectives that help students build energy
conception in a specific context.
Teaching and learning research on thermochemistry
Many present surveys of teachers and students in both high schools and universities show
students’ misconceptions in learning concepts related to thermochemistry. We can divide them into
four kinds: (1) misconceptions about energy changes in reactions. Students usually confuse
5
macroscopic and microscopic energy concepts. For example when explaining the relationship
between energy change and chemical bonds, students may agree that bonds forming require
energy and bonds breaking release energy. (2) Regarding thermal effects, it is a typical
misconception that endothermic reactions must be heated to react. When assessing the thermal
effects of reactions, students may judge it on reaction conditions (Yuan Guoqiang, 1989). (3)
About the unit: kJ﹒mol-1. For instance, the reaction 2CO(g)+O2(g)=2CO2(g); △H=-566 kJ•
mol-1, the value -566 kJ•mol-1means heat effect of per mole reaction, that is 2 mole carbon
monoxide reacts with 1 mole oxygen to form 2 mole carbon dioxide. It doesn’t mean 1 mole
carbon monoxide reacts to oxygen is able to produce 566kJ heat. Some supplementary materials
using the unit kJ replace kJ﹒mol-1 by mistake. This leads to difficulties in understanding the
concepts (Sheng Guoding, 2003; Li Wenfang, 2003). (4) About enthalpy and enthalpy change:
enthalpy is often described as the heat capacity of the system by university students (Beall, 1994).
It is difficult for most freshmen to distinguish enthalpy from heat or energy (Carson & Watson,
1999).
Content knowledge is one important perspective for energy research. We examine how ideas
of thermochemistry were development, how basic problems were discussed and how different
ways of thinking were presented in different textbooks and monographs to find out the core
content and knowledge shared among them. To understanding energy change of reactions, it is
necessary to know both the manifestation and reasons causing the energy change. Seen from the
heat of reaction perspective, energy change between a system and its surroundings, energy change
of reactions is caused by forming and breaking chemical bonds; seen from the enthalpy change
perspective, the change of system elements and thermodynamic states leads to energy change.
Heat of reaction and enthalpy change are the two core epistemic fields in learning energy change
of reactions (See Figure 4).
Figure 4. Epistemic model of energy change of system
6
Heats of reaction and ΔH of system are the main parts of thermochemistry in high school. In
order to obtain a functional epistemic model to guide teaching and learning, sub- models of heat of
reaction and ΔH of system should be further built.
a) Sub-model of heat of reaction
In this model, heat of reaction is considered as epistemic object and it can be structured by
three epistemic perspectives. Different perspectives show specific epistemic categories and levels
and can be seen from the epistemic results/performance (Table 2).
Table 2. Epistemic detailed model of heat of reaction
Sub-perspecti
Field
Perspective
Category /level
Results /performance
ve
Heat of
Microscopic
Reaction
Microscopic-
Know bond type variation phenomenon, know
reasons of
qualitative-
about some transition bond types, and understand
system
explain
bond types of reactants and products influence
energy
Bond type
energy changes.
7
changes
microscopic-
Explain energy changes using bond energy that is
qualitative-
energy required in chemical bonds breaking is not
explain
equal to energy produced in a bonds forming.
Microscopic-
Describe different expressions of bond energy,
quantitative –
calculate: enthalpy change by values of bond
explain
enthalpy: ΔrHm=ΣB.E.reactant-ΣB.E.product.
Macroscopic--
Calculate
heat of
quantitative –
calorimetric test, identify the importance of
reaction
explain
temperature changes in measure.
Measure
Macroscopic--
Describe the importance of controlling reaction
instrument
quantitative –
conditions, choose suitable calorimeter for a certain
design
condition.
Measure of
Bond energy
Q=ΔT·C
heat
of
reaction
by
Q=ΔT·C
in
Application
Syst
Endot
Quantitative –
Compare
of reaction
em
hermi
design
produced in different reactions, design and revise
heat
c
energy
conservation
and
the
heat
the course of production.
Exoth
Quantitative –
Calculate the heat that should be removed to
ermic
regulate
maintain the temperature for reaction control.
Sur-
Suppl
Quantitative –
Select reactions to reduce the temperature of
roun
y heat
design
surroundings.
ding
Get
Quantitative –
Design reaction course to increase the burning rate
heat
design
of fuels and use energy more scientifically.
In the epistemic field of reaction heat, the relationship of epistemic perspectives can be easily seen
in Figure 5.
Figure 5. The relationship of the epistemic perspectives in reaction heat
8
b) Sub-model of ΔH of system
In this model, ΔH of system is considered as epistemic field and it can be structured by three
epistemic perspectives (Table 3). And the relationship of these epistemic perspectives is shown in
Figure 6.
Table 3. Epistemic detailed model of ΔH of system
Category
Field
Perspective
Results /performance
/level
ΔH
system
of
ΔH
of
one
Thermochemical
Quantitative
equation
-describe
Write
thermochemical
equation
correctly
(including
states
and
temperatures) to express reaction heat, know the meaning of ΔH.
reaction
Quantitative
Explain how ΔH change when the coefficient in equation changes.
-explain
ΔH=ΣH(product
Quantitative
Understand enthalpy is an expression of system energy, calculate enthalpy
-explain
change by ΔH=ΣH(products)—ΣH(reactants)
s)—ΣH(reactants
)
Explain the system energy changes using enthalpy change.
9
Influen
Tempe
Qualitative-
ce
rature
describe
factors
Phase
Semi-quanti
Describe the relationship between matter states and ΔrH. Understand the
tative-descri
importance of marking matter states in thermochemical equation.
to ΔH
State the relationship between enthalpy change and temperature
be
Solven
Qualitative-
Describe solvent influence the value of enthalpy change. Mark the solvent
t
describe
in thermochemical equations.
ΔH in a group of reaction:
Qualitative-
Understand ΔrH can be influenced only by starting state and final state, no
Hess Law
describe
matter how complex the reaction course.
Quantitative
Calculate ΔrH of new reactions by known reaction ΔH
-explain
Quantitative
According to the known ΔH, design reaction course and calculate the ΔrH
-design
of new reactions.
Figure 6. The relationship of the epistemic perspectives in ΔH of system
10
Based on these models, tests and interviews were designed to diagnose the misconceptions
from high school students in learning thermochemistry. One of the most obvious problems is that
some students in senior high school still make errors in the calculation of heats of reaction and ΔH.
They cannot distinguish the system from the surroundings. It is hard for them to realize that Q and
ΔH are aimed at opposite systems. Students should be able, when given a change to a defined
system and its surroundings, to identify the direction of thermal energy transfer as either
endothermic or exothermic. To help solve this problem in teaching, first, we advise teachers to
build the concept of system and surroundings. Second, construct an energy diagram. It is an
effective simple strategy that helps students imagine the energy change.
Another problem we found in the interviews is in the ability to show significance of Hess’
law besides the calculation ΔH of a group of reactions. The epistemic performance level of most
students is “explain”, but they find it difficult to reach the level “design”. In class, teachers may
design activities and materials to guide students to determine the value of Hess law for
determining energy options. One example is using the question “How can we use coal more
scientifically?” as a leading question. In the class, teachers can let students investigate why coal
gasification and liquefaction replace traditional direct combustion in industrial production.
11
Students can practice through the calculation of Hess law and experience the significance at the
same time.
The epistemic field that students know develops from matter to reactions and then to system.
And the energy epistemic perspective deepens from temperature difference to reaction heat, then
to enthalpy change. In high school, the two core knowledge themes in thermochemistry learning
are heats of reaction and enthalpy change. In instructional design, these two should be of primary
concern. Also, the significance of thermal energy transformation should not be ignored in
teaching.
Research on the epistemic model of electrochemical cell
Chemical energy, heat, and electric energy can be interconverted into each other. In high
school chemistry, the focus is on the two directions of the conversion. The first focus is chemical
energy to heat and the second is chemical energy to electric energy. The primary cell is a typical
model needed to understand the process, and it presents teaching challenges for secondary high
school science teachers.
Present research shows that researchers stress conceptual understanding and misconceptions.
It seems that students have the ability to solve quantitative problems related to electrochemistry,
but few can answer the qualitative questions involving conceptual understanding (Viola I.Briss &
D. Rodney TNaX, 1999). Electrochemistry learning includes calculation and conceptual ideas. But
students typically have difficulties with the conceptual ideas (Mansoor& Eleazar, 2003). Michael J.
Sanger and Thomas J. Greenbowe (1999) selected 10 university textbooks to collect sentences and
tables which may lead to misunderstanding of concepts, and presented some teaching suggestions.
Some surveys indicate that the difficulties students have in understanding the primary
electrochemical cell may come from these aspects: (1) identification of the anode and cathode; (2)
the need for a standard half-cell; (3) direction of electrons path; (4) direction of electric current
path in primary cells and electrolytic cells; and (5) prediction of cell potentials and reaction
product (Garnett & Treagust, 1992; Michael & Thomas, 1997).
The research helps us in knowing how students learn these ideas and the challenges they have, but
it is necessary to analyze the related content in textbooks of high school and universities to build a
key content system about primary electrochemical cells teaching and learning, and relate it to how
students build understanding. Then the epistemic model can be constructed (Table. 4). In the table,
the terms “describe”, “explain”, and “apply” are separately selected with the
Macroscopic/microscopic, qualitative/quantitative, and unsystematic/systematic to express
different levels in each perspective.
Table. 4 Detailed epistemic model of electrochemical cell
Field
perspective
Sub-perspectiv
Category /level
Results /performance
e
Potential
difference
Electrode
reaction
Matter
Changes
Macroscopic/micr
oscopic
Qualitative/
quantitative
describe

Describe the
electrodes
explain

Analyze the direction of electrons
transfer
describe

Realize
the
quantitative
relationship in electrode reaction
Know that electrodes have

phenomenon
12
on

explain



apply


Energy
transformation
Qualitative/
quantitative
describe


explain


apply


Electrolyte
ionic diffusion
Qualitative/
quantitative
describe


explain


different activities that cause the
transfer of electrons
Understand electrons transfer from
the perspective of potential
difference.
Write reaction equations of
electrodes and the cell.
Analyze the transfer of electrons
from structure of reactants.
Predict the production and electron
number by charge conservation
law.
Choose electrode reactions and
cell reactions according to
conditions
Choose electrode reaction pair
according to potential difference.
Know energy transformation in
primary cell.
Describe the energy relationship
between reactants and products.
Explain energy transform from the
view of redox reactions separately
in cell.
Use the relationship between
Gibbs free energy and potential
difference to analyze the direction
of cell reaction.
Give some suggestions to raise
energy transform rate.
Predict the limit of energy
transformation in a cell
quantitatively.
Understand the form of potential
difference
based
on
ionic
diffusion.
Know the relationship between ion
concentration
and
potential
difference
Analyze how transmission rates of
different ions influence the liquid
(junction) potential.
Use Nernst equation to discuss the
relationship of cell potential and
13
ion concentration.
apply


ionic
equilibrium
Unsystematic-stati
cs
/systematicdynamic
describe


Describe the category of ions
Describe the movement of ions
based on electric neutrality.
explain

Analyze the movement of ions
only in one kind of cells.
Analyze the transfer of ions in a
few kinds of cells.

apply
Closed
circuit
Electronic
conductor
wire
Electrode
material
Qualitative
Unsystematic/syst
ematic


Choose
suitable
electrolyte
according to electrode reactions
Choose
suitable
electrolyte
according to cell reaction and
conditions
describe

Know wire is the road of electrons
explain

Analyze the transfer direction of
electrons
apply

Use wires to build a closed circuit
describe

Know electric charges move in/out
of electrode materials
explain

Explain the function of electrode
materials only when they involved
in the electrode reaction
Explain the function of electrode
materials whether they involved in
the electrode reaction or not

apply


Ionic conductor
Unsystematic/syst
ematic
Choose supporters of electrolyte
(electrolytic bridge or film)
according to conditions.
Choose the suitable concentration
of electrolyte according to
potential.
Choose electrode materials to
build the closed circuit based on
electrode reactions.
Choose electrode materials to
build the closed circuit based on
both electrode reactions and other
conditions.
describe

Describe how the movement of
ions helps to form the closed
circuit.
explain

Explain the function of ions in
electrolyte only when they
14

apply


involved in the electrode reaction
Explain the function of ions in
electrolyte whether they involved
in the electrode reaction or not
Using electrolyte solution, build a
closed circuit when designing a
primary cell
Using different supporters of
electrolyte, build a closed circuit
when designing a primary cell.
According to the model, we designed assessment tools that measured senior students’
cognitive development regarding primary electrochemical cells. The instrument had good
reliability and validity, which could be used for large-scale test. Our research shows there is a
hierarchical development concerning high school students’ epistemic system at present. This
demonstrates that our model is scientific. Meanwhile, chemistry learning and course sequencing
affect the epistemic model and its development.
Based on the above, our study proposes some suggestions for high school primary cell teaching.
After comparing with textbooks, we came up with advice in terms of teaching. Figure 7 is a
teaching model about cells resembling a coordinate system, which has two dimensions: principle
and device. Inside the coordinate system, the analysis process such as identification of the anode
and cathode, direction of electrons path, direction of electric current path, reactant and reaction
product, can all be shown clearly. It is a functional model that is not only for teaching, but also for
learning and even for assessment.
Figure 7. A teaching model for electrochemical cells
Research on curriculum content of quantum mechanics based on energy conception
Why quantum mechanics? On the one hand, to answer this question “what is energy”, we
have to deepen our research into particles that constitute matter. Energy comes from the force
between particles in essence, including electrons and atomic nucleus. Quantum mechanics is the
basis for understanding these particles. It is reasonable to research curriculum content of quantum
mechanics in order to promote the understanding of energy.
On the other hand, understanding chemical substances and reactions from an energy
15
perspective forms the foundation of chemistry thinking, which helps students to explain chemical
phenomena and solve chemical problems. Also, students benefit from building correct conceptions
and improving scientific literacy. Under the new high school chemistry curriculum in Mainland
China, some energy concepts are introduced, such as energy level, ionizing energy,
electronegativity and so on. However, teachers and students don’t understand the value of these
concepts. Some surveys show that most high school teachers and students lack understanding of
energy associated with these ideas.
We believe that the energy conception is based on quantum mechanics and forms a unique
way of thinking. It is necessary to build an epistemic model to answer the questions of how the
curriculum content develops students’ energy conception. On the basis of analyzing textbooks
related to quantum mechanics and structural chemistry, four energy understanding objects were
established: atom, molecule, crystal, and chemical reaction mechanism. We built four epistemic
models to explore students’ understanding, including epistemic perspectives, levels and
performances.
Seen from an energy perspective, one of the epistemic fields, the system of the atom, has
three epistemic perspectives: particles in an atom and their relationships, atomic properties, and
electron movement (Figure 8). These three are not independent, but are linked to each other.
Figure 8. The epistemic perspectives of the atom system based on energy conception
Knowing about the static structure of atom first will help build a better a dynamic structure
understanding. Both the static and dynamic structure of the atom help explain atomic properties.
And the dynamic structure, that is electrons movement, is essentially linked.
Molecules can also be seen from energy perspective (Figure 9). One epistemic perspective
has several sub-perspectives, and shows different epistemic levels. The model shows a thinking
path. The perspective that electrons in individual atoms is the basis for us to understand the
molecule system. Movement of electrons in a molecule is the key point to understand properties of
16
molecules. The property of molecules is a major theme in chemistry learning. It can be seen from
a variety of energy values.
Figure 9. The epistemic perspectives of molecule based on energy conception
Similar to the epistemic perspective regarding molecules, the epistemic perspective regarding
crystals include: particles in a repeating lattice structure and their relationship, electrons in subsystem before forming crystals, the movement of electrons in crystals, and properties of crystals.
The first two perspectives are the starting point of research on crystals
Research on chemical reaction mechanisms uses three main points: orbit theory, theories of
energy and energy level diagram of molecular orbital (MO). First is the MO of reactants and
products molecules, and the second is the movement of electrons among molecules. The third one
is the problems about reaction processes, like mechanism, conditions, activation energy and
transition state. These three points become the epistemic perspectives of chemical reaction
mechanisms. (Figure 10)
17
Figure 10. The epistemic perspectives of molecule based on energy conception
When building the perspectives of the above four epistemic fields – atomic, molecular,
crystalline, and chemical reaction mechanisms – the implication of these ideas are: (1) in the
quantization of energy, the smallest unit is hv; (2) the interaction of the old system results in a new
system, electronic configuration renewal, and energy change (generally, energy of the new system
is lower than the old one); (3) in determining effective interaction between orbits, whether MO or
AO, three principles must be followed, that is matching of orbitals symmetry, similar energy and
maximum overlap; and (4) electrons on orbits follow the law of lowest energy, Pauli exclusion
principle, and Hunt Rules.
The epistemic category/level includes from macroscopic/microscopic, qualitative/semiquantitative/quantitative understanding. Sometimes a new energy indicator means reaching a
higher level. For instance, orbital wave function and orbital energy formula are quantitative marks.
We believe that for high school students, thinking paths and the basic conception of quantum
mechanics are the two core epistemic ways of energy understanding, much more important than
specific knowledge. The first aim of quantum mechanics learning in high school is introducing
new theories, which lead to application. The 21st Century is a time of quantum mechanics, and it
is necessary for students to know about it, whether or not they major in college chemistry. The
second goal of the study of quantum mechanics is building a basic thinking path of property
research. When studying the property of atoms, students will realize that the properties are the
performance of its own structure. Students can use electron movement as well as particles in an
atom and their relationships to explain a specific property. This reminds students to recall previous
chemistry learning. The third target is understanding basic quantum mechanics. For high school
students, difficult knowledge like valence band is not as useful as the basic conception like orbital
and quantization. This orbital is generalized to mean not a line but continuous motion of atoms,
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molecules or electrons, and so on. About these particles, the continuous motion provides more
information, such as about energy and angular momentum. The greatest differentiation between
movement of these particles and the macroscopic world is quantization. In quantum mechanics,
the orbital is a representation of the motion of particles, and the information about these particles
such as energy and angular momentum is shown by four quantum numbers n/l/m/ms. It should be
emphasized that specific knowledge serves basic conceptions.
Discussion
Worthwhile theories and results of research on teaching and learning have to be accepted by
teachers and students and applied in class. The epistemic models we raised are the results of
practice, and in turn serve practice more. We raise this to explain the process of cognition, reveal
the learning map, and changes when students acknowledge specific concepts. By an epistemic
model, we are able to explain the students’ development from two perspectives, gaining new
epistemic perspectives and changing epistemic categories. A model is a detailed learning map of a
specific concept. It is possible to predict the performance of students when they have learned new
concepts. The model provides a basis for instructional design not only for researchers, but also for
teachers.
Under the big idea, energy, we focus on what is energy and energy transfer/transformation.
Specifically, three themes in the high school curriculum emerge: thermochemistry,
electrochemistry and quantum mechanics. These three themes serve as the research objects in
which we want to answer these questions with respect to energy teaching and learning: 1) what
should students learn; 2) what should students learn at different grade levels; and 3) how should
these various ideas be taught. Every epistemic model shows various perspectives, categories/levels
and results/performances, and reveals the essence hidden behind students’ performance in learning.
It also helps teachers in designing key questions to use during class, choose strategies to use
during class, and design assessments; in essence, it help teachers develop pedagogical content
knowledge with respect to teaching energy at various grade levels.
Our research on chemical energy transforming to thermal energy and electric energy has
covered curriculum and teaching practices. In thermochemistry learning, the energy epistemic
perspective deepens from temperature difference to heat of reactions, then to enthalpy change. In
senior high school, the core in thermochemistry learning is enthalpy change. This should be the
focus of instructional design. The microscopic cause of chemical energy is essential knowledge,
that is “energy is always required to break chemical bonds, and energy is always produced when a
bond is formed.” Also, the significance of thermal energy transformation should not be ignored in
teaching. In electrochemistry, potential difference and a closed circuit are the two necessary
components to an electrochemical cell. In learning and teaching, two dimensions, principle and
device are two key points. The principle that chemical reactions in electrochemical cell, is caused
by potential difference is a critical idea for students to understand. Devices ensure a closed circuit.
The analyzing processes of identification of the anode and cathode, direction of electrons path,
direction of electric current path, and the identification of the reactants and reactions product can
be shown clearly in these two dimensions. But we still lack research on teaching practices related
to the teaching and learning of quantum mechanics, which is one direction of study for us.
For future study, we propose to use epistemic models to analyze energy misconceptions in
specific topics, and provide advice on conceptual change learning and teaching strategies in detail.
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