Carbon: Transformations in Matter and Energy Environmental Literacy Project Michigan State University Systems and Scale Unit Activity 5.1 Molecular Models for Methane Burning Image Credit: Craig Douglas, Michigan State University

The bottom of flame at atomic-molecular scale Credits: Craig Douglas, Michigan State University Show students slides 2-5 to observe an ethanol flame at the macroscopic and atomic-molecular scale. Pose the question: “What’s the hidden chemical change when methane burns?” Explain to students that both methane and O2 enter the flame at the bottom. Oxygen Carbon Dioxide Water Methane Nitrogen

The top of flame at atomic-molecular scale Credits: Craig Douglas, Michigan State University Show students slides 2-5 to observe an ethanol flame at the macroscopic and atomic-molecular scale. Pose the question: “What’s the hidden chemical change when methane burns?” Explain to students that both methane and O2 enter the flame at the bottom. Oxygen Carbon Dioxide Water Methane Nitrogen

What happened between the bottom and the top of the flame? Bottom of the flame Top of the flame Oxygen Carbon Dioxide Water Methane Nitrogen Credits: Craig Douglas, Michigan State University Show students slides 2-5 to observe an ethanol flame at the macroscopic and atomic-molecular scale. Pose the question: “What’s the hidden chemical change when methane burns?” Explain to students that both methane and O2 enter the flame at the bottom. Show slides 4 and 5 to contrast the molecules at the bottom and top of a flame.

What’s the hidden chemical change when methane burns? Credits: Craig Douglas, Michigan State University Show students slides 2-5 to observe an ethanol flame at the macroscopic and atomic-molecular scale. Pose the question: “What’s the hidden chemical change when methane burns?” Explain to students that both methane and O2 enter the flame at the bottom. Show slides 4 and 5 to contrast the molecules at the bottom and top of a flame. Oxygen Carbon Dioxide Water Methane

Three Questions Poster Rules to Follow Connecting Atoms to Evidence 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. Show slide 6 to remind students that explaining chemical changes always involves answering the Three Questions. Divide students into pairs or small groups and have them practice answering the Three Questions in a new context. Remind them that the same rules about matter and energy apply for methane and ethanol.

Making the Reactant Molecules: Methane and Oxygen The flame of burning methane comes when ethanol (CH4) reacts with oxygen (O2). Make a molecules of methane and oxygen on the reactant side of your Process Tool for Molecular Models 11 x 17 Poster: Get the atoms you will need to make your molecules. Can you figure out from the formula for methane how many C, H, and O atoms you will need? Use the bonds to make models of an ethanol molecule (CH4) and at least 2 oxygen molecules (O2, with a double bond) Identify the high-energy bonds (C-C and C-H) by putting twist ties on them. How many high energy bonds does a molecule of methane have? Compare your molecules to the pictures on the next slide. Are they the same? This is an optional step. If you feel that your students can explain methane burning and answer the Three Questions, skip to activity 5.3. Divide the class into pairs and give each pair a molecular model kit, a set of Forms of Energy Cards, and Molecular Models 11 x 17 Placemat. Pass out one copy of 5.1 Molecular Models for Methane Worksheet to each student. Use slide 7 to show instructions to construct oxygen and methane molecules. Students can also follow instructions in Part B of their worksheet.

Chemical change Methane Oxygen Photo of reactant molecules: CH4 (methane) and O2 (oxygen) 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. Chemical change Methane Photo Credit: Michigan State University Use slide 8 to instruct students to compare their own molecules with the picture on the slide. Oxygen Reactants 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)

Important: When you are finished constructing the reactants, put all extra pieces away. Use slide 9 shows an important message: after students create their reactant molecules, make sure they put away all unused pieces of their molecule kits. This helps reinforce that the matter and energy in the reactants are conserved through the chemical change, and that only the materials from the reactants are used to build the products.

Rearranging the Atoms to Make Product Molecules: Carbon Dioxide and Water The flame of burning methane comes when methane (CH4) reacts with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O). Show how this can happen: 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 methane molecule and oxygen. Figure out numbers of molecules: How many O2 molecules do you need to combine with one methane molecule? How many CO2 and H2O molecules are produced by burning one molecule? Remember, atoms last forever. So you can make and break bonds, but you still need the same atoms. Remember, energy lasts forever. What forms of energy do the twist ties represent now? Compare your molecules to the pictures on the next slide. Are they the same? Show slide 10 of the PPT and have students re-arrange the atoms to make molecules of CO2 and H2O. To do this, they will need to move their molecules from the reactants side to the products side of the 11 x 17 Placemat. Explain to students that atoms last forever, so they should not add or subtract atoms when they change the reactant molecule into product molecules.

Water Chemical change Carbon dioxide Photo of product molecules: H2O (water) and CO2 (carbon dioxide) 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. Water Chemical change Carbon dioxide Photo Credits: Michigan State University Show students Slide 11 to compare the products and a comparison between reactants and products. Reactants 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)

Comparing photos of reactant and product molecules 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. Water Chemical change Carbon dioxide Methane Photo Credits: Michigan State University Show students Slide 12 to overview the entire process. Oxygen Reactants 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)

What happens to atoms and energy when methane burns? Carbon Dioxide Methane Reactants Chemical change Credits: Craig Douglas, Michigan State University (Optional) Have students watch an animation of the chemical change. Show slides 13-18 in the PPT to help students make connections between what is happening in the animation and the molecular models they made. For each slide, focus on different atoms and forms of energy and how they change. The animation draws attention to where they atoms begin and end in the reaction. Water Products Oxygen Heat and light energy

What happens to carbon atoms when methane burns? Carbon Dioxide Methane Reactants Chemical change Credits: Craig Douglas, Michigan State University (Optional) Have students watch an animation of the chemical change. Show slides 13-18 in the PPT to help students make connections between what is happening in the animation and the molecular models they made. For each slide, focus on different atoms and forms of energy and how they change. The animation draws attention to where they atoms begin and end in the reaction. Water Products Carbon atoms in methane become part of carbon dioxide molecules. Oxygen Heat and light energy 14

What happens to oxygen atoms when methane burns? Carbon Dioxide Methane Reactants Chemical change Credits: Craig Douglas, Michigan State University (Optional) Have students watch an animation of the chemical change. Show slides 13-18 in the PPT to help students make connections between what is happening in the animation and the molecular models they made. For each slide, focus on different atoms and forms of energy and how they change. The animation draws attention to where they atoms begin and end in the reaction. Water Products Oxygen atoms become part of carbon dioxide and water molecules. Oxygen Heat and light energy

What happens to hydrogen atoms when methane burns? Carbon Dioxide Methane Reactants Chemical change Credits: Craig Douglas, Michigan State University (Optional) Have students watch an animation of the chemical change. Show slides 13-18 in the PPT to help students make connections between what is happening in the animation and the molecular models they made. For each slide, focus on different atoms and forms of energy and how they change. The animation draws attention to where they atoms begin and end in the reaction. Water Products Hydrogen atoms become part of water molecules. Oxygen Heat and light energy

What happens to chemical energy when methane burns? Carbon Dioxide Methane Reactants Chemical change Credits: Craig Douglas, Michigan State University (Optional) Have students watch an animation of the chemical change. Show slides 13-18 in the PPT to help students make connections between what is happening in the animation and the molecular models they made. For each slide, focus on different atoms and forms of energy and how they change. The animation draws attention to where they atoms begin and end in the reaction. Water Products Chemical energy is transformed into heat and light energy. Oxygen Heat and light energy

What happens to atoms and energy when methane burns? Carbon Dioxide Methane Reactants Chemical change Credits: Craig Douglas, Michigan State University (Optional) Have students watch an animation of the chemical change. Show slides 13-18 in the PPT to help students make connections between what is happening in the animation and the molecular models they made. For each slide, focus on different atoms and forms of energy and how they change. The animation draws attention to where they atoms begin and end in the reaction. Water Products Oxygen Heat and light energy

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 methane burns? (Optional) Help students write a balanced chemical equation. Tell students that now that they have represented a chemical equation using molecular models and in animations, they will represent chemical change by writing the chemical equation. Show Slide 19 of the presentation to guide students through the process of writing a balanced chemical equation for the combustion of ethanol. Tell students that these rules apply to all chemical reactions. Tell students to write their equations in Part C of their worksheet. Have students write their own chemical equations before comparing them with the one on Slide 21.

Chemical equation for methane burning CH4 + 2O2  CO2 + 2 H2O (in words: methane reacts with oxygen to yield carbon dioxide and water) (Optional) Help students write a balanced chemical equation. Tell students that now that they have represented a chemical equation using molecular models and in animations, they will represent chemical change by writing the chemical equation. Show Slide 19 of the presentation to guide students through the process of writing a balanced chemical equation for the combustion of ethanol. Tell students that these rules apply to all chemical reactions. Tell students to write their equations in Part C of their worksheet. Have students write their own chemical equations before comparing them with the one on Slide 21.