is the viscosity (kgm-1s-1) η is related to the velocity of the particles and mean free path: = η η It can therefore be shown that , d-2 and is proportional to η Thermal Conductivity Energy flows from hot bodies to cold bodies until the temperature (or kinetic energy) of the molecules is equalised. The rate of heat flow fE in a gas (Jm2s-1) is proportional to the temperature gradient fE = κ is the thermal conductivity (JK-1m-1s-1) κ is related to the velocity of the particles and their mean free path: = κ κ It can therefore be shown that , d-2 and is proportional to κ Summary of transport properties of gases Transport Property Rate of Transfer Constant of Proportionality Diffusion fn = D D = Viscosity fp = = η η Thermal Conductivity fE = = κ κ Lesson 7 THE BEHAVIOUR OF REAL GASES Observing deviations from gas behaviour Compressibility factor Most gases only obey the ideal gas laws at a limited range of pressures and temperatures generally low – pressure and high temperature. In ideal gases, = 1 If gas behaviour is not observed, however, then is not equal to 1 and is given a value known as the compressibility factor (z). At low temperatures and reasonably high pressures, the attractive forces between the particles need to be considered these forces cause the V to be lower than expected for a particular P and cause P to be lower than – expected for a particular V. These factors cause PV to be lower than expected (ie PV < nRT and z < 1); at low temperatures and relatively high pressures, z < 1. At very high pressures, the size of the particles themselves becomes a consideration; the larger the particles, the less space there is in which for them to move. When this factor is significant, P is larger than expected for a
η is the viscosity (kgm-1s-1) η is related to the velocity of the particles and mean free path: η = It can therefore be shown that η is proportional to , d-2 and Thermal Conductivity Energy flows from hot bodies to cold bodies until the temperature (or kinetic energy) of the molecules is equalised. The rate of heat flow fE in a gas (Jm2s-1) is proportional to the temperature gradient fE = κ κ is the thermal conductivity (JK-1m-1s-1) κ is related to the velocity of the particles and their mean free path: κ = It can therefore be shown that κ is proportional to , d-2 and Summary of transport properties of gases Transport Property Rate of Transfer Constant of Proportionality Diffusion fn = D D = Viscosity fp = η η = Thermal Conductivity fE = κ κ = Lesson 7 THE BEHAVIOUR OF REAL GASES Observing deviations from gas behaviour Compressibility factor Most gases only obey the ideal gas laws at a limited range of pressures and temperatures – generally low pressure and high temperature. In ideal gases, = 1 If gas behaviour is not observed, however, then is not equal to 1 and is given a value known as the compressibility factor (z). At low temperatures and reasonably high pressures, the attractive forces between the particles need to be considered – these forces cause the V to be lower than expected for a particular P and cause P to be lower than expected for a particular V. These factors cause PV to be lower than expected (ie PV < nRT and z < 1); at low temperatures and relatively high pressures, z < 1. At very high pressures, the size of the particles themselves becomes a consideration; the larger the particles, the less space there is in which for them to move. When this factor is significant, P is larger than expected for a
chem_211_unit_1_notes.docx