F331- Developing Fuels Revision Essay Example
Developing Fuels * All gases take up the same volume under the same conditions. AT room temperature and room pressure this volume is 24 dm3. * Number of moles= volume in dm3 24 * Balanced equations can also be used to work out gas volumes. In the equations: 2Na + 2H2O 2NaOH + H2, where 15g of sodium is reacted, you can work out the volume of gas from working out the number of moles in 15g Na = 0.65 mol. Then you see that 2 mol of Na 1mol of H2, Thus 0.65 mol Na 0.325 mol H2. 0.325 x 24 = 7.8dm3. * Entropy tells you how much disorder there is in a substance. It is a measure of ways the particles can be arranged. Solids hare ordered so have low entropy, liquids have some disorder, so more entropy, and gases are random and so the entropy is high. * Substances like disorder. Particles will naturally move to give a substance the maximum possible entropy. * Increasing the number of particles increases the entropy as they are a greater number of ways in which the particles can be arranged. SA mixture of two different types of particles also has higher entropy than the equal number of one type of particle. * Enthalpy Change (ΔH) is the heat energy transferred in a reaction at constant pressure. The units of ΔH are in kJ mol-1. All chemical reactions have enthalpy changes. * The reactions can be exothermic or endothermic. Exothermic reactions give out energy, and thus the ΔH is negative. Endothermic reactions absorb energy, thus ΔH is positive. Combustion is exothermic and thermal decomposition is endothermic. * Enthalpy changes can be calculated using average bond enthalpies. To break bonds, energy is needed, thus ΔH is positive. To make bonds, energy is released, thus ΔH is negative. * The enthalpy change for a reaction is the overall effect of these two changes. If you need more energy to break bonds then is released when bonds are made, ΔH is positive. If it’s less, ΔH is negative.
Enthalpy Change of Reaction=Total Energy
Enthalpy Change of Reaction=Total Energy