Gas Laws

Kinetic theory Particles in all forms of matter are in constant motion A gas is composed of particles, usually molecules or atoms. The particles in a gas move rapidly inconstant random motion. All collisions are perfectly elastic.

Physical behavior of a gas depends on: volume temperature pressure

Volume How much space occupied volume of a gas in a sealed container is the volume of the container gases not in sealed containers are uncontained Units can be milliliters, liters, cubic centimeters

Temperature Measure of the average kinetic energy of particles in a substance same temperature = same average kinetic energy temperature measured using Kelvin scale Kelvin temperature = 0°C + 273 no upper limit for temperature lower limit = absolute zero 0 K = -273°C (no motion of particles)

To convert from Celsius to Kelvin—add 273 To convert from Kelvin to Celsius– subtract 273

Pressure force per area result of simultaneous collisions of billions of gas particles units of pressure atmospheres mm Hg Torr Pascal

Standard Temperature and Pressure (STP) Standard temperature = 0°C = 273 K Standard pressure = 1 atm = 760 mm Hg = 760 Torr = 101 kPa

Avogadro’s Law equal volumes of gases at the same temperature and pressure contain equal numbers of particles at STP 1 mole (6.02 X 1023 particles) of any gas occupies 22.4 liters

Boyle’s Law For a given mass of gas at constant temperature, the volume of the gas varies inversely with pressure. in other words, if pressure goes down, volume goes up and vice versa P1V1 = P2V2

Charles’ Law The volume of a fixed mass of gas is directly proportional to its Kelvin temperature if the pressure is kept constant in other words, if temperature increases, volume increases and vice versa V1 = V2 T1     T2

Gay-Lusaac’s Law P1 = P2 T1 T2 The pressure of a gas is directly proportional to the Kelvin temperature if the volume is kept constant. in other words, if temperature increases, pressure increases and vice versa P1 = P2 T1     T2

Combined Gas Law P1V1 = P2V2 T1 T2 Combines Boyle’s Law, Charles’ Law, and Gay-Lusaac’s Law into one P1V1 = P2V2 T1         T2

Dalton’s Law of Partial Pressures At constant volume and temperature the total pressure exerted by a mixture of gases is equal to the sum of the partial pressure of each gas. Ptotal = P1 + P2 + P3 ….. As soon as you see the words ‘over water’ in a problem, begin looking for P1 to subtract vapor pressure out of it and T1 which tells you the temperature to look up in the table so you will know how much to subtract.

Ideal Gas Law PV = nRT n = number of moles R = ideal gas constant T = temperature in Kelvins P = pressure V = volume if pressure is in atmospheres     R = 0.0821 atm L                                                                        k mol if pressure is in mm Hg or torr         R = 62.36 mm Hg                                                                        k mol if pressure is in kPa                  R = 8.287 kPa L                                                                     k mol