General Chemistry - Hour 17 - The Gas Laws

An attempt to explain why or how behavior or properties are as they are. It’s based on empirical evidence.

An attempt to explain gas behavior based upon the motion of molecules

Force of gas molecules colliding with surfaces

As the # of molecules increase, their collision with container surfaces increase, thus pressure increase. Pressure is directly proportional to the # of molecules (P ∝ n)

An volume (gas container) increase, the further the gas molecules travel (to hit the surface), thus decrease in pressure. Pressure is inversely proportional to the volume [P ∝ (1/V)]

Proportional to the average kinetic energy of the molecules.

As temperature increases, pressure increases. Pressure is directly proportional to the temperature (P ∝ T)

Pressure due to the layers of air in the atmosphere. As altitude increases, atmospheric pressure decreases.

A container will expand or contract until the pressure inside = atmospheric pressure outside. Expansion will lower the internal pressure. Contraction will raise the internal pressure. (Volume and pressure are inversely related)

Container explodes!

1. Identify quantities by their units
2. Write known and unknown quantities symbolically
3. Choose equation based upon list of quantities
4. Plug quantities into equation and solve.

1 atm = 101300 Pa = 101.3 kPa = 760 mm Hg = 14.7 psi (pounds per square inch)

Temperature scale used in gas calculations. Has an absolute zero. °C + 273 = K

1 atm (or anything it’s equal to) and 0°C (273 K)

experimental observations of the gas behavior that the Kinetic Molecular Theory explains.

The ratio of moles of a specific molecule to the total moles. No units for mole fractions

1 mole of any gas = 22.4 liters

• Use 1 mole = 22.4 L as an equivalent in the stoichiometry to find volume of the gas at STP. • Use a gas law to convert to desired temperature and/or pressure if the question asks for non-STP conditions.

all assumptions of the kinetic molecular theory are true.

Mnemonic: Phony Vampires are Not Real Things

grams per mole for a molecule

mass per volume of a sample [D= (m/V)]

Two of the KMT assumptions that molecules have no attractions/repulsions and that the particle volume is insignificant are not valid in real gas

The rate at which a gas travels through a container (e.g perfume sprayed in a room)

The rate at which a gas escapes through a tiny hole (e.g air leakage from a balloon overnight)

Rates of diffusion and effusion are inversely proportional to molecular mass. The heavier the molecules, the slower the rate