Jenny Dauer, Hannah Miller, Charles W. (Andy) Anderson

Michigan State University

 Conservation of energy: An analytical tool for student accounts of carbon-transforming

processesEnergy Summit, Michigan State University

December 16, 2012 

What forms and transformations of energy are most important for students to understand?

One sequence stands out as particularly significant: Carbon-transforming processes1.Sunlight2.Photosynthesis 3.Chemical energy in organic materials4.Cellular respiration, combustion, (fermentation)5.Energy we rely on for life and economic processes

– Life processes: growth, movement, body functions (this pathway accounts for 99.9%+ of all energy for life processes in all organisms)

– Human economic activities: production and distribution of food, transportation, housing, electrical power (this pathway accounts for 90%+ of energy for all human economic activities

6.Thermal energy7.Infrared radiation into space (affected by greenhouse gases)

What do informed citizens need to understand about energy in carbon-transforming processes?

• Energy in life processes– Basic life processes

• Why do plants need sunlight to grow?• How does exercise help us lose weight?

– Energy flow in ecosystems• Why do ecosystems have more herbivores than carnivores?• How do our eating choices (more or less meat) affect the human

population that the Earth can support?

• Energy in human economic activities– Why does CO2 concentration in the atmosphere keep

increasing?– How can zero-emission electric vehicles cause CO2

emissions?– How could biofuels reduce the amount of CO2 going into

the atmosphere?

Carbon TIME Units

Six units in development for National Geographic website:

1.Systems and Scale

2.Animals

3.Plants

4.Decomposers

5.Ecosystems

6.Human Energy Systems

A Key Learning Performance

Tracing matter and energy through familiar macroscopic phenomena that include carbon-transforming processes•Plant growth

– Plants in the light– Plants in the dark

•Animal growth•Animal movement•Decay (bread mold)•Combustion

Neither necessary nor sufficient for understanding

• Traditional physics problems: “A frictionless roller coaster is pulled to a height of 20 m….”

• Quantitative treatments of chemical energy: “Use Hess’s Law to calculate ΔH for the reaction….”

• Subatomic interpretations of energy: [From the NGSS Framework, p. 123-4] “These relationships [among macroscopic forms of energy] are better understood at the microscopic scale, at which all of the different manifestations of energy can be modeled as either motions of particles or energy stored in fields (which mediate interactions between particles).”

Three Issues in Teaching about Energy in Living Systems

1. Understanding the purpose of the concept of energy: energy as cause vs. energy as a tool for analysis.

2. Identifying forms of energy in living systems: identifying cause, vitality, or growth vs. limiting analysis to scientific forms of energy (chemical energy, light, heat, work or motion).

3. Tracing energy separately from matter: developing a sense of necessity in accounting for matter and energy as separate entities.

Learning Progression Research: Interview Tree Growth Question

• INTERVIEWER: …What is the difference between the things that give the tree energy and things that don’t give the tree energy?

• STUDENT A: Because things that give the tree energy they are what make it grow so like the water and the nutrients and the sun and the carbon … since they’re like the food for the tree it is the tree’s energy. And I think it has to do with the cells, like the cells need it for the tree to live.

• INTERVIEWER: Okay. And what about things that don’t give the tree energy? You know what kinds of things that that would not include?

• STUDENT A: Well certain animals like those caterpillars that eat the tree down.

Written Mouse Die Question

A) What kinds of energy are stored in the living mouse? Where did they come from?•Student B: The energy that the living mouse had stored is the food he had ate. He also might have slept and that made him wake up with energy.

B) What kinds of energy are stored in the dead mouse (if any)? How are they connected to the energy in the living mouse?•Student B: There is no energy in the dead mouse. If there were any he would still be alive.

Solutions and Simplifications

• Problem: Students think of energy as what causes events or enables actors (trees, mice, people) achieve their purposes rather than as a limiting resource that constrains systems

• Solution: Tell them what to do– Define a good explanation as answering the

Three Questions– They have to follow the rules

Three Questions Poster

Question Rules to Follow Evidence to Look For

The Movement Question: Where are atoms moving?

Where are atoms moving from?Where are atoms going to?

Atoms last forever in combustion and living systems

All materials (solids, liquids, and gases) are made of atoms

When materials change mass, atoms are moving

When materials move, atoms are moving

The Carbon Question: What is happening to carbon atoms?

What molecules are carbon atoms in before the process?

How are the atoms rearranged into new molecules?

Carbon atoms are bound to other atoms in molecules

Atoms can be rearranged to make new molecules

The air has carbon atoms in CO2

Organic materials are made of molecules with carbon atoms

• Foods• Fuels• Living and dead plants and

animals

The Energy Question: What is happening to chemical energy?

What forms of energy are involved?

How is energy changing from one form to another?

Energy lasts forever in combustion and living systems

C-C and C-H bonds have more stored chemical energy than C-O and H-O bonds

We can observe indicators of different forms of energy

• Organic materials with chemical energy

• Light• Heat energy• Motion

Three Issues in Teaching about Energy in Living Systems

1. Understanding the purpose of the concept of energy: energy as cause vs. energy as a tool for analysis.

2. Identifying forms of energy in living systems: identifying cause, vitality, or growth vs. limiting analysis to scientific forms of energy (chemical energy, light, heat, work or motion).

3. Tracing energy separately from matter: developing a sense of necessity in accounting for matter and energy as separate entities.

Student vs. Scientific Conceptions of Energy

Solutions and Simplifications

Limit accounts to four simplified forms of energy:1.Light energy: input to photosynthesis, but not infrared radiation going into space2.Heat energy: we do not distinguish between heat as an energy transfer process and thermal energy. 3.Work or motion energy: we do not distinguish between work as an energy transfer process and kinetic energy; we also do not clearly define “work.”4.Chemical energy: we describe chemical energy as “stored” in high-energy (C-H and C-C) and released when C-C and C-H bonds are replaced with lower energy C-O and H-O bonds

Three Issues in Teaching about Energy in Living Systems

1. Understanding the purpose of the concept of energy: energy as cause vs. energy as a tool for analysis.

2. Identifying forms of energy in living systems: identifying cause, vitality, or growth vs. limiting analysis to scientific forms of energy (chemical energy, light, heat, work or motion).

3. Tracing energy separately from matter: developing a sense of necessity in accounting for matter and energy as separate entities.

An Example Question

A potato is left outside and gradually decays. One of the main substances in the potato is the starch amylose: (C6H10O5)n. What happens to the atoms in amylose molecules as the potato decays? Choose True (T) or False (F) for each option.

T F Some of the atoms are converted into nitrogen and phosphorous: soil nutrients.

T F Some of the atoms are consumed and used up by decomposers.

T F Some of the atoms are incorporated into carbon dioxide.T F Some of the atoms are converted into energy by

decomposers. (94% of college students, mostly science majors, multiple institutions, said True)

T F Some of the atoms are incorporated into water.

Solutions and Simplifications

• Something we are careful about:– Energy is released by change from high-energy

to low-energy bonds, NOT by breaking bonds

• Deliberate simplifications– Define CO2 and H2O as low-energy “base state”– Focus on oxidation of C and H rather than

reduction of O (justification: organic carbon is limiting reactant)

– Quasi-quantitative accounting for twist-ties as “energy units”

Scaffolding Inquiry and Accounts

Evidence of CO2 in air from burning4 minutes 8 minutes

10 minutes, with control

Results for Ms. Angle’s Class

•How do your results compare with the results for Ms. Angle’s class?

Trial #

Initial mass of ethanol

(g)

Final mass of ethanol

(g)

Change in mass

of ethanol

(g)

start BTB

colorend BTB

color1 24.00 22.97 -1.03 blue yellow2 20.63 19.43 -1.20 blue yellow3 33.22 32.54 -0.68 blue yellow4 27.23 26.59 -0.64 blue yellow5 32.01 31.21 -0.80 blue yellow

6 27.37 26.73 -0.64 blue yellow

Answering the Three Questions for Ethanol Burning

What are your ideas?•The Movement Question: Where atoms moving? (Where are atoms moving from? Where are atoms going to?)•The Carbon Question: What is happening to carbon atoms? (What molecules are carbon atoms in before the process? How are the atoms rearranged into new molecules?)•The Energy Question: What is happening to chemical energy? (What forms of energy are involved? How is energy changing from one form to another?)

ZOOMING INTO A

What’s the hidden chemical change when ethanol burns?

Driving question

Movement of ethanol burning at macroscopic scalesc

ales

Material identity and transformationMatter

EnergyEnergy forms and transformation

Matter MovementAll filtersAnalyzi

ng Back to blank

Atomic molecular

Macroscopic

Large scale

Microscopic

The bottom of flame at atomic-molecular scale

The top of flame at atomic-molecular scale

What happened between the bottom and the top of the flame?

Bottom of the flame

Top of the flame

Comparing photos of reactant and product moleculesStart by making the molecules and energy units of the reactants and putting them on the reactants side, then rearrange the atoms and energy units to show the products.

Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can’t add or subtract atoms)Energy lasts forever (so you can change forms of energy, but energy units can’t appear or go away)

Reactants Products

Chemical changeEthanol with chemical energy

OxygenHeat Light

Water

Carbon dioxide

What happens when ethanol burns?

Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can’t add or subtract atoms)

Energy lasts forever (so you can change forms of energy, but energy units can’t appear or go away)

What forms of energy are in the reactants?

What molecules are carbon atoms in before the change? What other molecules are involved?

Where are atoms moving from?

What forms of energy are in the products?

What molecules are carbon atoms in after the change? What other molecules are produced?

Where are atoms moving to?

Chemical change

Key Features of Approach

• Learning progression framework and assessments

• Start with familiar macroscopic processes– Inquiry into transformations of matter and energy– Atomic-molecular explanations– Place in large-scale systems

• Tell students the rules (Three Questions)• Account for matter first• Quasi-quantitative accounting for energy

units

Criteria for an Appropriate Simplification

• Is it comprehensible to students?

• Is understanding achievable within reasonable constraints on instructional time?

• Does it position students to understand more sophisticated models in their future learning?

Thanks to Funders

This research is supported in part by grants from the National Science Foundation: Learning Progression on Carbon-Transforming Processes in Socio-Ecological Systems (NSF 0815993), and Targeted Partnership: Culturally relevant ecology, learning progressions and environmental literacy (NSF-0832173), CCE: A Learning Progression-based System for Promoting Understanding of Carbon-transforming Processes (DRL 1020187), and Tools for Reasoning about Water in Socio-ecological Systems (DRL-1020176). Additional support comes from the Great Lakes Bioenergy Research Center. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation or the United States Department of Energy

Thanks to Contributors to this Research

• Hui Jin, Jing Chen, Li Zhan, Josephine Zesaguli, Hsin-Yuan Chen, Brook Wilke, Hamin Baek, Kennedy Onyancha, Jonathon Schramm, Courtney Schenk, Jennifer Doherty, and Dante Cisterna at Michigan State University

• John Moore, Shawna McMahon, Andrew Warnock, Jim Graham, Kirstin Holfelder, Colorado State University

• Alan Berkowitz, Eric Keeling, Cornelia Harris, Cary Institute of Ecosystem Studies

• Ali Whitmer, Georgetown University• Dijanna Figueroa, Scott Simon, University of California, Santa

Barbara• Laurel Hartley at the University of Colorado, Denver• Kristin Gunckel at the University of Arizona• Beth Covitt at the University of Montana• Mark Wilson, Karen Draney, Jinnie Choi, and Yong-Sang Lee

at the University of California, Berkeley.

Extra Slides

How Atoms Bond Together in Molecules

• Atoms in stable molecules always have a certain number of bonds to other atoms:– Carbon: 4 bonds– Oxygen: 2 bonds– Hydrogen: 1 bond

• Oxygen atoms do NOT bond to other oxygen atoms if they can bond to carbon or hydrogen instead.

• Chemical energy is stored in bonds between atoms– Some bonds (C-C and C-H) have high chemical energy– Other bonds (C-O and O-H) have low chemical energy

Making the Reactant Molecules: Ethanol and Oxygen

The flame of burning ethanol comes when ethanol (C2H5OH) reacts with oxygen (O2). Make a molecules of ethanol and oxygen on the reactant side of your Molecular Models poster:•Get the atoms you will need to make your molecules. Can you figure out from the formula for ethanol how many C, H, and O atoms you will need?•Use the bonds to make models of an ethanol molecule (C2H5OH) and at least 3 oxygen molecules (O2, with a double bond)•Identify the high-energy bonds (C-C and C-H) by putting twisty ties on them. How many high energy bonds does a molecule of ethanol have?•Compare your molecules to the pictures on the next slide. Are they the same?

Photo of reactant molecules: H2CO3 (carbonic acid)Start by making the molecules and energy units of the reactants and putting them on the reactants side, then rearrange the atoms and energy units to show the products.

Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can’t add or subtract atoms)Energy lasts forever (so you can change forms of energy, but energy units can’t appear or go away)

Reactants Products

Chemical changeEthanol with chemical energy

Oxygen

Rearranging the Atoms to Make Product Molecules: Carbon Dioxide and Water

The flame of burning ethanol comes when ethanol (C2H5OH) reacts with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O). Show how this can happen:1.The heat of the flame breaks the bonds in the molecules, so their bonds can break. Now they can recombine into carbon dioxide (CO2) and water vapor (H2O). Make as many of these molecules as you can from one ethanol molecule.2.Figure out numbers of molecules:

– How many O2 molecules do you need to combine with one ethanol molecule?– How many CO2 and H2O molecules are produced by burning one molecule?

3.Remember, atoms last forever. So you can make and break bonds, but you still need the same atoms.4.Remember, energy lasts forever. What forms of energy do the twisty ties represent now?5.Compare your molecules to the pictures on the next slide. Are they the same?

Photo of product molecules CO2 and H2O (carbon dioxide and water)Start by making the molecules and energy units of the reactants and putting them on the reactants side, then rearrange the atoms and energy units to show the products.

Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can’t add or subtract atoms)Energy lasts forever (so you can change forms of energy, but energy units can’t appear or go away)

Reactants Products

Chemical change

Heat Light

Water

Carbon dioxide

Writing a Chemical Equation• Chemists use chemical equations to show how atoms of

reactant molecules are rearranged to make product molecules

• Writing the equation in symbols: Chemists use an arrow to show how reactants change into products:[reactant molecule formulas] product molecule formulas]

• Saying it in words: Chemists read the arrow as “yield” or “yields:”[reactant molecule names] yield [product molecule names]

• Equations must be balanced: Atoms last forever, so reactant and product molecules must have the same number of each kind of atom

• Try it: can you write a balanced chemical equation to show the chemical change when ethanol burns?

Chemical equation for ethanol burning

C2H5OH + 3O2 2 CO2 + 3 H2O

(in words: ethanol reacts with oxygen to yield carbon dioxide and water)

Website and Questions

http://edr1.educ.msu.edu/EnvironmentalLit/publicsite/html/tm_cc.htmlIncludes•Assessments at middle school, high school, college level•Teaching materials from earlier projects•Carbon TIME teaching materials

– Systems and Scale, Plants in a couple of weeks– Ecosystems, Bioenergy later this year

Message from a teacher

“I am having a problem with some of the CTime content.  They claim that C-C and C-H bonds are high energy and C-O and O-H bonds are low energy.  I cannot in good conscience teach that.”

C-H 98O-H 110C-C 80C-O 78H-H 103C-N 65O=O 116 (2 x 58)C=O 187* (2 x 93.5)C=C 145 (2 x 72.5)

Calculating Bond Energies

All bond energies are NEGATIVE CH4 (4*-98 kcal) + 2O2 (2*-116 kcal) --> CO2 (2*-187 kcal) + 2H2O (4*-110 kcal) Total bond energies:-624 kcal for the reactants -834 kcal for the products: 210 kcal released as heat and light.

Note that:•Hess’s Law basically restates Conservation of Energy•Students can solve Hess’s Law problems correctly without realizing they have the signs backward (procedural display again)

Learning Progressions Include:

• A learning progression framework, describing levels of achievement for students learning

• Assessment tools that reveal students’ reasoning: written assessments and clinical interviews

• Teaching tools and strategies that help students make transitions from one level to the next

The Role of Scale and Principles in Scientific Accounts

• Connecting scales:– Macroscopic scale: plant growth, growth and

functioning of consumers and decomposers, combustion as key carbon transforming processes

– Atomic-molecular scale: photosynthesis, cellular respiration, combustion, digestion and biosynthesis

– Large scale: carbon reservoirs and fluxes in earth systems, affected by human populations and technologies

• Key principles– Conservation of matter: Carbon atoms gotta go

somewhere– Conservation of energy– Degradation of energy (matter cycles, energy flows)

Contrasts between Force-dynamic and Scientific Discourse (Pinker, Talmy)

• Force-dynamic discourse: Actors (e.g., animals, plants, machines) make things happen with the help of enablers that satisfy their “needs.”– This is everyone’s “first language” that we have to

master in order to speak grammatical English (or French, Spanish, Chinese, etc.)

• Scientific discourse: Systems are composed of enduring entities (e.g., matter, energy) which change according to laws or principles (e.g., conservation laws)– This is a “second language” that is powerful for

analyzing the material world• We often have the illusion of communication

because speakers of these languages use the same words with different meanings (e.g., energy, carbon, nutrient, etc.)