Unit 7Gas Laws

Gases• Gases (g): Transparent,

compressible, expand without limit, have no shape/volume. **Take the shape and volume of their container.

Gases exert pressure: STP: defined as standard temperature and pressure*Found on Table A 1atm 101.3kPa*Pressure can also be 760 torr or 760 mm Hg

Kinetic Molecular Theory of GasesIdeal Gas Laws

• Ideal gases are those whose gas particles (molecules):

travel in random, constant, straight line motion. (*At absolute zero, all kinetic energy ceases, so all particles stop moving.)

are separated by great distances relative to the size of the molecule so that the volume of the actual molecule is considered negligible.

have no real attractive forces between them.

have collisions that may result in the transfer of energy between particles {but remember overall energy is conserved}

ENERGY

Real Gases• Real gases do have volumes and do

exhibit attractive forces between their particles or we would have no atmosphere!

For real gases to behave like ideal gases:

Temperature must be highPressure must be low

The two most common real gases that behave most like ideal gases are H2 and He because they are the smallest and least dense

Avagadro’s Hypothesis• under the same conditions of

temperature and pressure, 2 equal volumes of two different gases will have the same number of particles regardless of their masses. • At STP, this number of particles is

Avogadro’s number, which is 6.02 x 1023

The Combined Gas Law• The pressure a gas exerts on its surroundings is

related to its temperature and volume such that:• FORMULA: P1V1 = P2V2

T1 T2*note* Temperature must be in KELVIN!!! Pressure

1 and 2 and Volume 1 and 2 must be in the same units.

See examples

Boyle’s Law• As long as temperature remains

constant, pressure and volume of a gas will affect each other inversely • FORMULA: P1V1 = P2V2

• See example

Charles Law As long as the pressure on a given

mass of a gas remains constant, the temperature and volume will affect each other directly.

FORMULA: V1 = V2

T1 T2

See example

Temp

Vol

Gay-Lussac’s Law• As song as the volume of a given mass of a gas

remains constant, the temperature and pressure will affect each other directly.

FORMULA: P1 = P2

T1 T2

• To graph this relationship: Pressure

Temp