OPTION C: ENERGY C.1 ENERGY SOURCES By: Merinda Sautel Alameda Int’l Jr/Sr High School Lakewood, CO msautel@jeffco.k12.co.us ESSENTIAL IDEA Societies are completely dependent on energy resources. The quantity of energy is conserved in any conversion but the quality is degraded. NATURE OF SCIENCE (2.2) Use theories to explain natural phenomena—energy changes in the world around us result from potential and kinetic energy changes at the molecular level. Energy has both quantity and quality. INTERNATIONAL-MINDEDNESS The International Energy Agency is an autonomous organization based in Paris which works to ensure reliable, affordable and clean energy for its 28 member countries and beyond. The International Renewable Energy Agency (IRENA), based in Abu Dhabi, UAE, was founded in 2009 to promote increased adoption and sustainable use of renewable energy sources (bioenergy, geothermal energy, hydropower, ocean, solar and wind energy). THEORY OF KNOWLEDGE “I have no doubt that we will be successful in harnessing the sun’s energy. If sunbeams were weapons of war we would have had solar energy centuries ago.” (Lord George Porter). In what ways might social, political, cultural and religious factors affect the types of research that are financed and undertaken, or rejected? There are many ethical issues raised by energy generation and its consequent contributions to pollution and climate change. What is the influence of political pressure on different areas of knowledge? UNDERSTANDING/KEY IDEA C.1.A A useful energy source releases energy at a reasonable rate and produces minimal pollution. USEFUL ENERGY • Energy is defined as the ability to do work. • The Law of Conservation of Energy states that energy can neither be created nor destroyed. It can only be converted from one form to another. The problem is that the “quality” of our energy is being degraded. If we lose energy to the environment, it is no longer available to do useful work. USEFUL ENERGY • An energy source needs to be cheap, plentiful, and readily accessible and provide high-quality energy at a suitable rate – not too fast or too slow. • A fuel is a substance that can release energy by changing its chemical or nuclear structure. UNDERSTANDING/KEY IDEA C.1.B The quality of energy is degraded as heat is transferred to the surroundings. Energy and materials go from a concentrated into a dispersed form. The quantity of the energy available for doing work decreases. UNDERSTANDING/KEY IDEA C.1.C Renewable energy sources are naturally replenished. Non-renewable energy sources are finite. APPLICATION/SKILLS Be able to discuss the use of different sources of renewable and non-renewable energy. RENEWABLE VS NON-RENEWABLE • A renewable source of energy is one that is replenished at a greater rate than it is used up. Hydroelectric dam – replenished by rainfall Wood for fuel – replaced by growing trees Solar and wind energy/fuel cells/biomass/geothermal • A non-renewable source of energy is one that is not replenished as it is used up. Coal – millions of years for fossil fuels to form UNDERSTANDING/KEY IDEA C.1.D Energy density=energy released from fuel volume of fuel consumed UNDERSTANDING/KEY IDEA C.1.E Specific energy=energy released from fuel mass of fuel consumed ENERGY DENSITY SPECIFIC ENERGY • Specific factors need to be taken into consideration for storage and transport of a fuel. Energy density – energy produced per unit volume Specific energy – energy produced per unit mass • These are inter-related via the density of the fuel. • Specific energies and energy densities are never negative values. APPLICATION/SKILLS Be able to determine the energy density and specific energy of a fuel from the enthalpies of combustion, densities and the molar mass of fuel. EXAMPLE 1 The enthalpies of combustion of a range of organic compounds are given in section 13 of the IB Data Booklet. Calculate the specific energy and energy density of hexane from its density which is 0.6548 g/cm 3 under standard conditions. What info do you need? 1. Formulas for compound and formulas for specific energy & energy density found in IB Data Booklet. 2. Molar mass 3. Heat of combustion from IB Data Booklet EXAMPLE 1 - WORKED Hexane is C6H14 with a molar mass of 86.2 g/mol. It’s enthalpy of combustion is -4163 kJ/mol. We are given the density of 0.6548 g/cm 3. What do we need? Specific energy=energy released mass of fuel Make the UNITS work out in thermo problems. From the formula above we need kJ/g. How do we get these units from the given information? EXAMPLE 1 - WORKED If we divide the enthalpy of combustion by the molar mass, we will have the correct units. -4163 kJ x mol = 48.3 kJ/g which is specific energy mol 86.2g Now we need - Energy density =energy released vol of fuel From this formula, we need kJ/cm 3 so multiply the specific energy by the density. 48.3kJ x 0.6548 g = 31.6 kJ/cm3 which is energy density g cm3 EXAMPLE 2 The standard enthalpy of combustion of carbon is -394 kJ/mol. The density of anthracite, one of the purest coals, is 2267 kg/m3. Use this information to calculate the energy density and specific energy of this form of coal. Specific energy = 32.8 kJ/g Energy density = 7.44 x 10 7 kJ/m3 EXAMPLE 3 Ethanol is a fuel produced from plant products by fermentation. It has a density of 789 g/dm 3 and its enthalpy of combustion is -1367 kJ/mol. Calculate energy density and specific energy. Write a balanced equation for the combustion of ethanol and state the amount, in mol, of carbon dioxide produced per mole of ethanol burned. Why is this considered “green or renewable” chemistry even though it produces CO 2 in the combustion reaction. EXAMPLE 4 The enthalpies of combustion of methane and hydrogen are given in section 13 of the IB data booklet. a). Calculate the specific energies of CH 4 and H2. b). Use the ideal gas equation to calculate the density of the two gases at STP and hence calculate the energy density of the two gases. c). Identify the best fuel based on this information and discuss the practical difficulties involved in its widespread use. APPLICATION/SKILLS Be able to discuss how the choice of fuel is influenced by its energy density or specific energy. • Nuclear fuels have the highest specific energies followed by fossil fuels which are higher than renewable sources. • The higher the specific energy, the better the fuel source, but this has to be balanced with renewable vs non-renewable considerations. UNDERSTANDING/KEY IDEA C.1.F The efficiency of an energy transfer = useful output energy x 100 total input energy ENERGY EFFICIENCY • A primary source of energy is often not used but converted to a secondary source such as electricity and some energy is lost in this conversion. • No matter how well a power plant is designed it can never convert energy from one form to another with 100% efficiency. • The efficiency is usually less than 50%. APPLICATION/SKILLS Be able to determine the efficiency of an energy transfer process from appropriate data. EXAMPLE 5 A coal-burning power station generates electrical power at a rate of 5.50 x 108 J/s. The power station has an overall efficiency of 36% for the conversion of heat into electricity. a. Calculate the total quantity of electrical energy generated in one year of operation. b. Calculate the total quantity of heat energy used in the generation of this amount of electricity. c. Calculate the mass of coal that will be burned in one year of operation, assuming that coal has the enthalpy of combustion of graphite. EXAMPLE 5 WORKED You need the formula: efficiency = useful output energy x 100 total input energy What are the givens? Efficiency = 36% and rate = 5.50 x 10 8 J/s Enthalpy of combustion = -394 kJ/mol a) Energy in one year: 5.50 x 108 J/s x 60s/min x 60 min/hr x 24 hr/day x 365 days/yr = 1.73 x 1016 J EXAMPLE 5 WORKED b) efficiency = useful output energy x 100 = 36% total input energy useful output energy = .36 total input energy You just calculated output energy in “a”. Rearrange the equation so input energy = output/.36 Input energy = 1.73 x 10 16 J/.36 = 4.82 x 10 16 J EXAMPLE 5 WORKED c) Heat energy = 4.82 x 1016 J = 4.82 x 1013 kJ To solve for moles, use the enthalpy of combustion. 4.82 x 1013 kJ x mol = 1.22 x 1011 mol 394kJ To solve for mass, multiply by the molar mass. 1.22 x 1011 mol x 12.01 g/mol = 1.47 x 1012 g EXAMPLE 6 4.00 x 107 kJ are required to heat a home in a typical winter month. a. The house can be heated directly with a gas boiler burning methane gas (efficiency 85%). Calculate the mass of methane required in one month using this method of heating. b. The home can also be heated using electricity from a natural gasburning power plant (efficiency 50%). Determine the mass of methane needed to generate the electricity needed to heat the house. *Please note that the input energy must be larger than the output energy. Use this rule of thumb when using the efficiency formula.* APPLICATION/SKILLS Be able to discuss the advantages and disadvantages of the different energy sources in C.2 through to C.8. CITATIONS International Baccalaureate Organization. Chemistry Guide, First assessment 2016. Updated 2015. Brown, Catrin, and Mike Ford. Higher Level Chemistry. 2nd ed. N.p.: Pearson Baccalaureate, 2014. Print. ISBN 978 1 447 95975 5 eBook 978 1 447 95976 2 Most of the information found in this power point comes directly from this textbook. The power point has been made to directly complement the Higher Level Chemistry textbook by Brown and Ford and is used for direct instructional purposes only.
