Properties of gases

a gas is a substance that has no well defined boundaries but diffuses rapidly to fill any container in whch it is placed

a gas differs from solids and liqquids beween gases do not have a fixed volume

the volume of a sample of gas depends on temeperature and pressure

temerpature

  • celcius scale

  • kelvin scale

  • 0K = 273.15 degrees

pressure

  • we must use pascal (pa) in our calculations

  • standard pressure = 1×10 (5) Pa

volume of gas varies with temperature and pressure

so when comparing volumes of gases, it is important to keep the temeorature and pressure constant

boyles law

  • P = 1/V for a fixed mass of gas at constant pressure

    charles law

  • V = T (kelvin) for a fixed mass of gas at constant pressure

  • it is consistant with PV = nRT due to constant

avagadros law

  • under the same condition of temperature andpressure, equal volumes have the same number of molecules

gay lussacs law of combining volumes

  • the volume of reacting gases and their gas products are in small whole number ratios when at the same temperaure and pressure

molar volume calculations

  • the gas occupied by 1 mole of any gas is called molar volume

  • standard temperature and pressure (stp) or room temperature and pressure (rtp) are 2 units often used in chemistry

  • volume(i) = no. moles x STP

  • volume (i) = no. moles x RTP

the kinetic theory of gases

  1. there are no attractive or repulsive forces between molecules of gas

  2. gas molecules are so small and so widely seperated that the actual volume of all the molecules is negligable compared with the space that they occupy

  3. collisions between particles are perfectly elastic i.e there is no loss of kinetic energy in these collisions although there may be a transfer of energy

ideal gas

  • a gas that perfectly obeys all the assumptions of kinetic theory under all conditions of temperature and pressure

limitations to the kinetic theory of gases

  • there are forces of attraction between gas molecules e.g Van Der Waals, dipole-dipole

  • the volume is not negligable under high pressure

real gases come close to an ideal gas under 2 conditions

  1. low pressure

  2. hugh temperatures. molecules are moving rapidly, preventing the forces between molecules from operating