# Comparing Fossil Fuel and Biofuel Combustion. Short Introduction Methane: A non-renewable fossil fuel gas pumped from deep below the Earth’s surface from.

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Comparing Fossil Fuel and Biofuel Combustion

Short Introduction Methane: A non-renewable fossil fuel gas pumped from deep below the Earth’s surface from both coal and oil deposits. A major component of biogas - a renewable fuel that is produced from decaying plant and animal manure. Ethanol: Renewable liquid biofuel produced from several different types of plant material. Octane: A non-renewable liquid fossil fuel which is the major component of gasoline refined from crude oil.

A Quick Review Carbon-based fuels such as wood, coal, and gasoline supply energy. These fuels release exothermic energy during a combustion chemical reaction. The energy has been stored within the bonds of the molecules. The energy is released because the chemical bond energy of the products are less than the chemical bond energy of the reactants. The products of most combustion reactions include water and carbon dioxide

Bond Energy between two atoms Use the information in Table 1 to determine the energy in the bonds of each of the different molecules. TABLE 1: BOND ENERGY VALUES BondEnergy (kJ/mole) C - H414.2 C - C347.3 O - H464.4 BondEnergy (kJ/mole) C - O357.7 H - H439.4 BondEnergy (kJ/mole) C = O803.2 O = O494.9

Calculating the Total Bond Energy of a molecule. TABLE 1: BOND ENERGY VALUES Structural Formula Bond Type Bond Energy (kJ/mole) # bonds in the molecule Total Bond Energy (kJ/mole) Methane: CH 4

Part A - Modeling Combustion Reactions 1. Use the model pieces to build each of the fuel molecules below. Draw the structural formula for each molecule. Hint: All bonds are single bonds. METHANE ETHANOL

Part A - Model the combustion of methane in the presence of just enough oxygen. 1. Make the models of the reactants: one CH 4 and two O 2 molecules. 2. Next model the breaking of the reactant bonds by removing all the white bonds from the atom of the three reactant molecules. 3. Finally, model the formation of the products by reassembling the six bonds and seven atoms from the “broken” reactant molecules to make as many water (H 2 O) and carbon dioxide (CO 2 ) molecules as you can.

Part A - Model the combustion of methane in the presence of just enough oxygen. Count up the number of H 2 O and CO 2 molecules you made and complete the chemical equation below that shows the combustion of methane. CH 4 + 2O 2 → CO 2 + 2H 2 O

Part A - Model the combustion of ethanol in the presence of more than enough oxygen. 1. Make the models of the reactants: one C 2 H 6 O and five O 2 molecules. 2. Next model the breaking of the reactant bonds of your C 2 H 6 O and just enough (but not all) of your O 2 molecules to make the products water (H 2 O) and carbon dioxide (CO 2 ) molecules. Hint: If you break apart more O 2 molecules than you need, reassemble them.

Part A - Model the combustion of ethanol in the presence of more than enough oxygen. Determine the number of O 2 molecules you needed to combust the single molecule of ethanol and count the number of water (H 2 O) and carbon dioxide (CO 2 ) molecules you produced. Use this data to complete the chemical equation that describes the combustion of ethanol. C 2 H 6 O + 3O 2 → 2CO 2 + 3H 2 O

Part A - Model the combustion of octane in the presence of oxygen. Octane, C 8 H 18, has a structure very similar to methane. Draw its structural formula.

Part A - Model the combustion of octane in the presence of oxygen. Below is the completed chemical equation that describes the combustion of octane. C 8 H 18 + 12.5 O 2 → 8CO 2 + 9H 2 O

Part A - Model the combustion of octane in the presence of oxygen. 1. Make the models of the reactants: one C 8 H 18 and one O 2 molecules. 2. Next model the breaking of the reactant bonds of your C 8 H 18 and your O 2 molecule to make the products 8 water (H 2 O) and 9 carbon dioxide (CO 2 ) molecules.

Part B - Calculating the Energy Released During Combustion Reactions Use the information in Table 1 to determine the energy in the bonds of each of the different reactant molecules. TABLE 1: BOND ENERGY VALUES BondEnergy (kJ/mole) C - H414.2 C - C347.3 O - H464.4 BondEnergy (kJ/mole) C - O357.7 H - H436.0 BondEnergy (kJ/mole) C = O803.3 O = O497.9

Part B - Calculating the Energy Released During Combustion Reactions Use the information in Table 1 to determine the energy in the bonds of each of the different REACTANT molecules. Structural Formula bond typebond energy (kJ/mole) # of bonds in the molecule Total bond energy (kJ/mole) H - C414.241656.8 METHANE

Part B - Calculating the Energy Released During Combustion Reactions Use the information in Table 1 to determine the energy in the bonds of each of the different REACTANT molecules. Structural Formula bond typebond energy (kJ/mole) # of bonds in the molecule Total bond energy (kJ/mole) H - C C - C C - O O - H 414.2 347.3 357.7 464.4 51115111 2070.0 347.3 357.7 464.4 ETHANOL

Part B - Calculating the Energy Released During Combustion Reactions Use the information in Table 1 to determine the energy in the bonds of each of the different REACTANT molecules. Structural Formulabond typebond energy (kJ/mole) # of bonds in the molecule Total bond energy (kJ/mole) H - C C - C 414.2 347.3 18 7 7455.6 2431.1 OCTANE

Part B - Calculating the Energy Released During Combustion Reactions Use the information in Table 1 to determine the energy in the bonds of each of the different REACTANT molecules. Structural Formulabond typebond energy (kJ/mole) # of bonds in the molecule Total bond energy (kJ/mole) O = O 497.91 OXYGEN

Part B - Calculating the Energy Released During Combustion Reactions Use the information in Table 1 to determine the energy in the bonds of each of the different PRODUCT molecules. Structural Formulabond typebond energy (kJ/mole) # of bonds in the molecule Total bond energy (kJ/mole) O = C = OC = O803.321606.6 CARBON DIOXIDE

Part B - Calculating the Energy Released During Combustion Reactions Use the information in Table 1 to determine the energy in the bonds of each of the different PRODUCT molecules. Structural Formulabond typebond energy (kJ/mole) # of bonds in the molecule Total bond energy (kJ/mole) H - O - HH - O497.92928.8 WATER

Part B - Calculating the Energy Released During METHANE Combustion Energy released = (total bond energy of products) - (total bond energy of all reactants) CH 4 + 2O 2 → CO 2 + 2H 2 O MoleculeBond energy per molecule (kJ/mole) # of moleculesTotal bond energy (kJ/mole) CH 4 1656.81 O2O2 497.92989.8 MoleculeBond energy per molecule (kJ/mole) # of moleculesTotal bond energy (kJ/mole) CO 2 1606.61 H2OH2O928.821857.6 REACTANTSREACTANTS PRODUCTSPRODUCTS Total Bond Energy in reactants = 2646.6 kJ/mole Total Bond Energy in products = 3464.2 kJ/mole

Part B - Calculating the Energy Released During METHANE Combustion Energy released = (total bond energy of products) - (total bond energy of all reactants) CH 4 + 2O 2 → CO 2 + 2H 2 O Products - Reactants = Energy Released 3464.2 - 2646.6 = 817.6 kJ/mole of methane combusted

Part B - Calculating the Energy Released During ETHANOL Combustion Energy released = (total bond energy of products) - (total bond energy of all reactants) C 2 H 6 O + 3O 2 → 2CO 2 + 3H 2 O MoleculeBond energy per molecule (kJ/mole) # of moleculesTotal bond energy (kJ/mole) C2H6OC2H6O3240.41 O2O2 949.931484.7 MoleculeBond energy per molecule (kJ/mole) # of moleculesTotal bond energy (kJ/mole) CO 2 1606.623213.2 H2OH2O928.832786.4 REACTANTSREACTANTS PRODUCTSPRODUCTS Total Bond Energy in reactants = 4725.1kJ/mole Total Bond Energy in products = 5999.6 kJ/mole

Part B - Calculating the Energy Released During ETHANOL Combustion Energy released = (total bond energy of products) - (total bond energy of all reactants) C 2 H 6 O + 3O 2 → 2CO 2 + 3H 2 O Products - Reactants = Energy Released 5999.6 - 4725.1 = 1274.5 kJ/mole of ethanol combusted

Part B - Calculating the Energy Released During OCTANE Combustion Energy released = (total bond energy of products) - (total bond energy of all reactants) C 8 H 18 + 12.5O 2 → 8CO 2 + 9H 2 O MoleculeBond energy per molecule (kJ/mole) # of moleculesTotal bond energy (kJ/mole) C 8 H 18 9886.71 O2O2 494.912.56186.25 MoleculeBond energy per molecule (kJ/mole) # of moleculesTotal bond energy (kJ/mole) CO 2 1606.6812852.8 H2OH2O928.898359.0 REACTANTSREACTANTS PRODUCTSPRODUCTS Total Bond Energy in reactants = 16,072.95kJ/mole Total Bond Energy in products = 21,212.0 kJ/mole

Part B - Calculating the Energy Released During OCTANE Combustion Energy released = (total bond energy of products) - (total bond energy of all reactants) C 8 H 18 + 12.5O 2 → 8CO 2 + 9H 2 O Products - Reactants = Energy Released 21,212.0 - 16,072.95 = 5139.0 kJ/mole of octane combusted

Analysis The three fuels from most to least energy released: MOST = octane (5139 kJ/mole) ethanol (1274.5 kJ/mole) LEAST = methane (817.6 kJ/mole) The three fuels from most to least CO 2 produced: MOST = octane (8 = coefficient number = moles) ethanol (2 = coefficient number = moles) LEAST = methane (1 = coefficient number = moles) Ratio of energy released to CO 2 methane = 817.6/1 = 817.6 kJ/mole ethanol = 1274.5/2 = 637.2 kJ/mole octane = 5139.0/8 = 642.4 kJ/mole Of all the three fuels analyzed in this activity, which do you think is the best? Explain METHANE - highest energy to CO 2 ratio

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