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

Unit Map You are here Use the instructional model to show students where they are in the course of the unit. Show slide 2 of the 5.1 Molecular Models for Methane Burning PPT.

The bottom of flame at atomic-molecular scale Credits: Craig Douglas, Michigan State University Remind students that the rules always apply. Tell students that if they can explain what happens when ethanol burns, they can also explain what happens when many other materials burn. That is because the same rules apply: matter and energy change in similar ways. Tell students that they will practice with another material: a natural gas called methane (CH4). Zoom into burning methane. Show students slides 3-6 to observe a methane 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 Nitrogen

The top of flame at atomic-molecular scale Credits: Craig Douglas, Michigan State University Zoom into burning methane. Show students slides 3-6 to observe a methane 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 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 Zoom into burning methane. Show students slides 3-6 to observe an methane 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 Zoom into burning methane. Show students slides 3-6 to observe a methane 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

Answer each of the questions (numbered 1-4) below to explain how matter and energy move and change in a system. Note that matter movement is addressed at both the beginning (1) and end (4) of your explanation. Question Where are molecules moving? How do molecules move to the location of the chemical change? How do molecules move away from the location of the chemical change? Evidence We Can Observe Moving solids, liquids, and gases are made of moving molecules. A change in mass shows that molecules are moving. Rules to Follow All materials (solids, liquids, and gases) are made of atoms that are bonded together in molecules. Scale: The matter movement question can be answered at the atomic- molecular, cellular, or macroscopic scale. Question How are atoms in molecules being rearranged into different molecules? What molecules are carbon atoms in before and after the chemical change? What other molecules are involved? Evidence We Can Observe BTB can indicate CO2 in the air. Organic materials are made up of molecules containing carbon atoms: • fuels • foods • living and dead plants and animals decomposers Rules to Follow Atoms last forever in combustion and living systems. Atoms can be rearranged to make new molecules, but not created or destroyed. Carbon atoms are bound to other atoms in molecules. Scale: The matter change question is always answered at the atomic- molecular scale. Have students practice answering the Three Questions for methane burning. Show slide 7 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. Evidence We Can Observe We can observe indicators of different forms of energy before and after chemical changes: • light energy • heat energy • chemical energy stored in organic materials • motion energy Question What is happening to energy? What forms of energy are involved? What energy transformations take place during the chemical change? Rules to Follow Energy lasts forever in combustion and living systems. Energy can be transformed, but not created or destroyed. C-C and C-H bonds have more stored chemical energy than C-O and H-O bonds. Scale: The energy change question can be answered at the atomic- molecular, cellular, or macroscopic scales.

Making the Reactant Molecules: Methane and Oxygen The flame of burning methane comes when methane (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 methane 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? Have students use the molecular model kits to make one methane and two oxygen molecules. This is an optional step. If you feel that your students can explain methane burning and answer the Three Questions, skip to activity 5.2. 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 8 to show instructions to construct oxygen and methane molecules. Students can also follow instructions in Part B of their worksheet. Use slide 9 to instruct students to compare their own molecules with the picture on the slide. Use slide 10 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. Accommodation: Do this optional activity. Arrange the molecules along with students so they have a step-by-step model of what the molecules should look like.  

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 Have students use the molecular model kits to make one methane and two oxygen molecules. This is an optional step. If you feel that your students can explain methane burning and answer the Three Questions, skip to activity 5.2. 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 8 to show instructions to construct oxygen and methane molecules. Students can also follow instructions in Part B of their worksheet. Use slide 9 to instruct students to compare their own molecules with the picture on the slide. Use slide 10 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. Accommodation: Do this optional activity. Arrange the molecules along with students so they have a step-by-step model of what the molecules should look like.   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. Have students use the molecular model kits to make one methane and two oxygen molecules. This is an optional step. If you feel that your students can explain methane burning and answer the Three Questions, skip to activity 5.2. 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 8 to show instructions to construct oxygen and methane molecules. Students can also follow instructions in Part B of their worksheet. Use slide 9 to instruct students to compare their own molecules with the picture on the slide. Use slide 10 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. Accommodation: Do this optional activity. Arrange the molecules along with students so they have a step-by-step model of what the molecules should look like.  

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? Have students complete the table on their worksheet for the reactants. When they have completed their reactants, tell students to complete the table about matter and energy in their worksheet for the reactants. Have students construct a model of the chemical change. Tell students to follow the instructions the worksheet to construct their products. Show slide 11 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. Show students Slide 12 to compare the products they made to the products on the slide. Show students Slide 13 to overview the entire process.

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 Have students construct a model of the chemical change. Tell students to follow the instructions the worksheet to construct their products. Show slide 11 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. Show students Slide 12 to compare the products they made to the products on the slide. Show students Slide 13 to overview the entire process. 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 Have students construct a model of the chemical change. Tell students to follow the instructions the worksheet to construct their products. Show slide 11 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. Show students Slide 12 to compare the products they made to the products on the slide. Show students Slide 13 to overview the entire process. Have students complete the table in their worksheet for the products. When they have completed their reactants, tell students to complete the table in their worksheet for their products. Have students verify that the number of atoms before and after remained constant: Atoms last forever! Tell students that this means that the number of atoms before and after the reaction does not change. 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 Have students watch an animation of the chemical change. Show slides 14-19 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 Have students watch an animation of the chemical change. Show slides 14-19 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. Focus on carbon atoms. Water Products Carbon atoms in methane become part of carbon dioxide molecules. Oxygen Heat and light energy 15

What happens to oxygen atoms when methane burns? Carbon Dioxide Methane Reactants Chemical change Credits: Craig Douglas, Michigan State University Have students watch an animation of the chemical change. Show slides 14-19 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. Focus on oxygen atoms. 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 Have students watch an animation of the chemical change. Show slides 14-19 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. Focus on hydrogen atoms. 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 Have students watch an animation of the chemical change. Show slides 14-19 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. Focus on chemical energy. 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 Have students watch an animation of the chemical change. Show slides 14-19 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? Help students write a balanced chemical equation. Tell students that now that they have represented a chemical change using molecular models and in animations, they will represent chemical change by writing the chemical equation. Show Slide 20 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) 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 20 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.