C.1-Energy Sources(Data Booklet 13) STP: 273k P:100kPa

Oil is the fossil fuel that currently provides the worlds economy with the most energy but this will change as our finite resources run out. Fossil fuels are non-renewable energy sources-they are used at a faster rate that they can be replaced Uranium is another non-renewable source of energy, which gives up energy as its nuclei splits to form smaller nuclei. Conservation of Energy: energy cannot bet created or destroyed. It can only change from one form into another. Although our energy resources are being run down, this is not happening to the quantity of energy in the universe. The problem is that the quality of our energy is being degraded-if we loose energy to the environment it is no longer available to do useful work. (In any cyclical process designed to convert heat to work, some energy is always degraded. Degraded energy is energy that is no longer available for the performance of useful work.) Sources of energy are either: Hot bodies (Sun) or Objects that store high quality of potential energy (water in reservoir or chemical energy of a fossil fuel). Energy needs to be cheap, plentiful and readily accessible and provide high-quality energy at a suitable rate (not too slow/not too fast). It should do this in a way that has a minimal effect on the environment. Rain Water: poor energy source, possesses gravitational potential energy but it releases it too slow at a rate to be useful. Nuclear Bomb: releases energy at too fast rate for it to be used safely. Current High Quality Sources: fossil fuels, nuclear fission, electrochemical cells, solar energy, biomass and alternative sources (wind, etc.). Fuel: is a substance that can release energy by changing its chemical or nuclear structure. Fossil fuels release energy chemical reaction Uranium releases energy during a fission reaction Renewable resources can be replenished at a rate faster than they are used (e.g. wood as trees can be grown to replace those chopped down to provide wood as a fuel). Chapter 5 combustion reaction/change enthalpy not relevant as factors such as storage and transport of a fuel are not considered within. (Enthalpies of combustion used for energy released) Energy density: energy produced per unit volume. (kJ/cm3) Specific energy: energy produced per unit mass. (kJ/g) Density: Fusion fuel 3 x 109

238U 9 x 109

Gasoline (petrol) 45.8

Natural gas 55.5

Coal 33.0

Wood 17.0

Hydrogen 142

Nuclear fuels have the highest specific energies (and energy density) and fossil fuels have higher specific energies that the related renewable sources. Energy conversions are never 100% efficient. A primary source of energy is often not used directly but converted to a secondary source such as electricity and some energy is lost during the conversion. Efficiency (of an energy transfer) = Fossil Fuel Typical efficiency values

Gas 40-50%

Oil 35-45%

Coal 35-40%

Generally, the efficiency is less than 50% as the random motion of the heated gas particles needs to be converted into the coordinated motion of the particle in the solid turbine and some energy is lost in the process.