Methane Burning: Atomic-Molecular Scale Transformations

1. Carbon: Transformations in Matter and Energy Environmental Literacy ProjectMichigan State University Systems and Scale UnitActivity 5.1 Molecular Models for Methane Burning

2. Unit Map You are here

3. The bottom of flame at atomic-molecular scale Oxygen Nitrogen Carbon Dioxide Water Methane

4. The top of flame at atomic-molecular scale Oxygen Nitrogen Carbon Dioxide Water Methane

5. What happened between the bottom and the top of the flame? Top of the flame Bottom of the flame Oxygen Nitrogen Carbon Dioxide Water Methane

6. What’s the hidden chemical changewhen methane burns? ? Oxygen Carbon Dioxide Water Methane

7. 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. • 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.

8. 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?

9. 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 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)

10. Important: When you are finished constructing the reactants, put all extra pieces away.

11. 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?

12. 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 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)

13. 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 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)

14. What happens to atoms and energy when methane burns? Carbon Dioxide Methane Reactants Chemical change Water Products Oxygen Heat and light energy

15. What happens to carbon atomswhen methane burns? Carbon Dioxide Methane Reactants Chemical change Water Products Carbon atoms in methane become part of carbon dioxide molecules. Oxygen Heat and light energy

16. What happens to oxygen atomswhen methane burns? Carbon Dioxide Methane Reactants Chemical change Water Products Oxygen atoms become part of carbon dioxide and water molecules. Oxygen Heat and light energy

17. What happens to hydrogen atomswhen methane burns? Carbon Dioxide Methane Reactants Chemical change Water Products Hydrogen atoms become part of water molecules. Oxygen Heat and light energy

18. What happens to chemical energywhen methane burns? Carbon Dioxide Methane Reactants Chemical change Water Products Chemical energy is transformed into heat and light energy. Oxygen Heat and light energy

19. What happens to atoms and energy when methane burns? Carbon Dioxide Methane Reactants Chemical change Water Products Oxygen Heat and light energy

20. 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?

21. Chemical equation for methane burning CH4 + 2O2 CO2 + 2 H2O (in words: methane reacts with oxygen to yield carbon dioxide and water)