3 Chemical reactions Reactions that release heat are exothermic Reactions that absorb heat from surroundings are endothermic
4 The energy involved in chemical reactions is measured in kilojoules per mole (kj/mol) The energy change of a reaction is represented by r H r H calculated using heats of formation on page 5 of data book
5 Elements are assigned a value of 0 for heat of formation - sign means an exothermic change + sign means endothermic change
6 For ammonia f H 45.9kJ / mol This means 45.9 kj of heat are released when 1 mol of NH 3 forms from N 2 and H 2
7 The energy change of a reaction is found by r H n f H 0 products n f H 0 reac tants Sum of sigma Number of moles Standard molar heat of formation See page 5
8 Example Determine the energy released in the reaction Use table to get values kj/mol 0 kj/mol kJ/mol kj/mol
9 1 mole 5 moles 3 moles 4 moles kj/mol 3(-393.5) 4( ) H n H products n H reac tants 0 0 r f f H 3( 393.5) 4( 241.8) ( 103.8) r r H kJ r H = 2044 kj is released (exothermic)
10 Example 6C (s) + 3H 2(g) C 6 H 6(l) (benzene) 0 kj/mol 0kJ/mol kj/mol r H n f H 0 products n f H 0 reac tants r H = kj (0 kj + 0 kj) r H = kj you must add energy to the reactants to make benzene (ENDOTHERMIC)
11 Example Determine the energy released in the combustion of butane gas, as represented by the equation above.
12 kj/mol H n H products n H reac tants 0 0 r f f H 8( 393.5) 10( 241.8) 2( 125.7) r r H kJ
13 Comparing Reaction Energy Nuclear reactions release much more energy than chemical reactions or phase changes
14 Example When 1 mole of water evaporates, it absorbs kj (Phase change) When 1 mol of water vapour forms from O 2 and H 2, it releases kj (Chemical change)
15 FUEL NEEDED FOR 1 YEAR OF POWER PLANT OPERATIONS
16 Renewable energy sources Wind, solar, geothermal, hydroelectric, tidal, biomass Usually considered to be environmentally friendly
17 Wind Wind is caused by the combination of the spinning of the planet on its axis and the uneven heating Earth s surface by the sun.
18 Pro Zero emissions: no CO 2, SO x, NO x, particulates, trace metals, or solid waste Phased growth: can increase production capacity as your needs grow Con High initial investment Intermittent: Wind must blow between 25 kph and 100 kph for power generation Distribution: turbines must be nearby existing transmission lines, or costs become very high.
19 Pro Con Small footprint: Wind turbine towers interfere little with surface activity (e.g., farming, livestock) Price stability: fossil fuel prices change due to international events, wind power comes with a relatively fixed price
21 Tidal energy Tidal energy is a renewable source of energy since it only uses the energy from rising and falling of the tides Gravitational potential energy is converted to electrical energy
22 Only about 20 locations have good inlets and a large enough tidal range (~3 m) to produce energy economically. 2 in operation: France and Bay of Fundy (Nova Scotia)
23 Biomass Energy stored in non-fossil organic materials such as wood, straw, vegetable oils and wastes from forest, agricultural and industrial sectors. derived from solar energy that has been stored in plants through the process of photosynthesis.
24 fossil fuels require thousands of years to be converted into usable forms biomass energy can be used in an renewable fashion. Municipal solid waste and sewage sludge can also be considered as biomass.
25 Doesn t contribute to greenhouse gas or CO 2 emissions because the plants absorb CO 2 from the air through photosynthesis which is released back into air when the plant is burned Biomass can be converted to methane or ethanol by bacteria and then burned (biomass digester)
27 Ethanol Ethanol made by fermenting biomass can be used as fuel is more expensive to produce when potential food supplies such as corn and wheat are used.
28 ethanol contains less energy per volume than gasoline typically get about 25-30% less distance per tank when fueled with blend of up to 85% ethanol (E85).
29 E-85 $0.69 per litre Gasoline $0.71 per litre
31 Biodiesel Biodiesel is an alternative fuel that is made from vegetable and animal oils. Rudolf Diesel, the inventor of the diesel engine, demonstrated in 1900 at the world s fair in Paris that an engine could run on peanut oil rather than petroleumbased fuels.
34 Geothermal energy is a renewable power source that comes from the heat generated by radioactive decay in the earth. Geothermal Energy
35 Geothermal power plants do not have to use an intermediate technology to produce steam to power the turbine generators. The land needed for geothermal power plants is smaller per megawatt than for almost any other type of power plant.
36 Geothermal power plant in New Zealand
37 Geothermal vent in Iceland
38 Underground temperatures for the northern portion of Alberta at 5 km depth
39 Alberta Geological Survey has estimated that the potential energy of the Alberta s geothermal waters is roughly equivalent two to five trillion barrels of oil. it is possible to convert abandoned well sites into a system of geothermal power generation plants around 20 MW
40 Ground Loop High-density polyethylene pipes are buried in ground and filled with a solution of antifreeze and water. This liquid absorbs heat from the earth and delivers it to a heat pump in the home.
41 Heat Pump Unit The heat pump compresses the fluid from the earth to temperatures that are hot enough to heat either air for forced air heating, or water for infloor radiant heating.
42 Distribution System Similar to conventional systems, geothermal heating can be distributed through either a forced air duct system, radiant infloor, or a combination of both.
43 Solar Energy Earth gets approximately 1,000 watts of energy per square metre. Radiant solar energy uses the light (EMR) from the sun to supply the potential energy
45 Solar Energy passive solar heating uses sun s energy to heat buildings In summer, the roof blocks most of direct sunlight from home, keeping it cool In winter, sunlight comes in and heat is absorbed by floor, etc
46 Solar Cells Convert sunlight into directly into electricity (photovoltaic cells) Sunlight knocks electrons out of atoms of a conductor which then flow along wires Produces DC Inefficient & are not good for highly energyintensive uses such as heating.
47 The brighter the light, the more current is produced Need a convertor to change DC into AC (most household devices use AC)
50 Solar-thermal solar thermal concentrates light to heat a liquid (~700 o C). this heat can then be used to create superheated steam, which drives conventional electric turbines.
51 Will this system work in Alberta? Why or why not?
52 Hydroelectric The energy of falling water is converted to electrical energy (E p E k electrical energy
53 Fission (Nuclear Energy) Uses uranium or plutonium Radioactive waste is a problem Provides the greatest amount of energy per kg of fuel
54 World Uranium Reserves Canada has the 3 rd largest reserves of uranium Canada produces 1/3 of world s uranium
55 Fusion No working fusion reactors yet Waste products are relatively harmless (helium and heat)
56 Why is coal slightly cheaper than natural gas?
57 Fuel cells H 2 (g) + O 2 (g) H 2 O + energy
58 Hydrogen gas is split into H + ions which releases electrons Electrons power a motor Is combined with O 2 from air to form water
59 Problem to obtaining H 2 gas Storing H 2 gas Short range for vehicles before refueling
60 Generators most sources of energy are used to turn a generator Converts potential energy into kinetic (mechanical) energy and then electrical energy A conductor is turned in a magnetic field
61 Generator A magnetic field will cause a current to flow in a moving conductor Called electromagnetic induction
62 The magnetic field exerts a force on electrons in the moving conductor (1) The electrons flow through the wire and are removed from the generator by the commutator (2) and brushes Converts mechanical (kinetic) energy to electrical energy An alternator produces AC
63 A motor can act as a generator Used in hybrid cars to recharge battery When brakes applied, the electric motor acts like a generator Driving: motor turns wheels Braking: wheels turn motor
64 Energy Consumption Per-capita energy consumption is totalenergy used in country number of peoplein country
68 Efficiency Compact Fluorescent Lightbulbs (CFLs) use about 75 percent less electrical energy than standard incandescent bulbs, for the same amount of light output output % efficiency 100% input
69 Example An 90 W incandescent light bulb is 15% efficient. If it uses 90 W of electricity, how much light energy does it emit?