Gases

gas pressure §

• pressure is defined as force per unit area
• gas particles exert pressure when they collide with the walls of their containers
• the SI unit of pressure is the pascal
• there are several units of pressure
  • pascal, kilopascal, atmosphere

temperature §

• average kinetic energy is directly proportionate to the Kelvin temperature
  • convert degC to K
  • K = degC + 273

standard temperature and pressure §

• STP standard temp = 0deg C or 273 K (changes to 25deg in Redox, not consistent over all chemistry fields.)
• standard pressure = 1atm = 7600mm Hg = 760 torr = 101.3 kPa

gas laws §

• the four properties of gases (amount of moles, pressure, volume, temperature)

boyle’s law §

• at constant temperature, the volume of the gas increases as the pressure increases. The volume of the gas decreases and the pressure increases.
• p1v1 = p2v2

charles law §

• at a constant pressure, the volume of a gas increases as the temperature of the gas increases and the volume decreases when the temperature decreases.
• $\frac{V_1}{T_1}=\frac{V_2}{T_2}$
• increase average kinetic energy.

gay-lussac’s law §

• pressure of a gas is directly proportional to its absolute temperature a constant volume
• $\frac{P_1}{T_1}=\frac{P_2}{T_2}$

ideal gas equation - combining the gas laws together §

• $PV=nRT$
• P = pressure (kPa)
• V = measured in litres.
• n = mole of gas (mol)
• R = gas constant (0.08314 if using litres, atm, mol and kelvin)
• T = temperature, must be in kelvin.

avogadros law §

• equal volume of gases at the same temperature and pressure contains equal number of molecules/1 mole of ANT gas takes up a volume of 22.71 L at STP.

applying kinetic energy §

• gases “diffuse” very quickly
  • diffuse mean: movement of particles from high concentration of area to low concentration of area.
  • gases are easily compressed due to large amount of space between particles
  • gases spread out to fill a container due to the negligible forces of attraction between particles.
  • gases exert pressure because the particles move rapidly and collide with the interior surfaces of the container.
  • gases have low densities due to large amount of space between particles.

why increasing temperature increases the pressure of gas in a sealed vessel. §

• increased average kinetic energy of gas particles.
• increase force of collisions on walls of the cotnainer.
• increased velocity/speed of particles.
• increases frequency of collisions with walls of container.

-> rates of reaction §

• rate of reaction increases as temperature increases.
  • if food is left in heat, it gets spoilt pretty quickly.
  • particles with kinetic energy higher than activation energy will have successful collisions.
  • force of collisions will be more significant with higher kinetic energy.

molar volume §

• stp fixed at convenient standard values, molar volume of a gas can be determined.
  • e.g. at stp, 1 mole of any gas occupies a volume of 22.71 litres, this is the molar volume.
  • n(CO2) = 5
  • volume occupied = no. moles x molar volume = 5 x 22.71 = 113.55 L