UNIT 8Gas Variables

Pressure

1. Caused by collisions between molecules and the walls of container.

2. Force per unit area; changing force of collisions or area changes pressure.

3. Units: 1 atm = 101.3 kPa = 760 mm Hg (torr) = 14.7 lbs/in2 (psi)

Volume

1. Determined by space between molecules. Molecules themselves are assumed to have no volume.

2. As molecules bounce more vigorously, spacing widens.

3. Units: mL, liters

Temperature

1. Directly proportional to average kinetic energy of molecules: 1⁄2mv2 = cT

2. Must be Kelvin for gas law calculations.

Amount

1. Perhaps surprisingly, number, not mass, of molecules determines gas properties.

2. Moles.

Avogadro’s Law: Volume and Number of moles are directly proportional.

Minor Gas Laws

Avogadro’s Law: Volume and Number of moles are directly proportional.

Minor Gas Laws

Avogadro’s Law: Volume and Number of moles are directly proportional.

Minor Gas Laws

V1n1

V2n2

Boyle’s Law: Pressure and Volume are inversely proportional.

Minor Gas Laws

Boyle’s Law: Pressure and Volume are inversely proportional.

Minor Gas Laws

V1P1 V2P2

Charles’ Law: Volume and Temperature are directly proportional.

Minor Gas Laws

Charles’ Law: Volume and Temperature are directly proportional.

Minor Gas Laws

V1T1

V2T2

Dalton’s Law: Pressure and Number of moles are directly proportional.

Minor Gas Laws

P1n1

P2n2

Gay-Lussac’s Law: Pressure and Temperature are directly proportional.

Minor Gas Laws

P1T1

P2T2

In summary…

Minor Gas Laws

The five minor gas laws can be combined by focusing on the one law that is different…

Combining the Gas Laws

Boyle’s LawP1V1=P2V2

P1n1

P2n2

P1T1

P2T2

V1n1

V2n2

V1T1

V2T2

This is called the COMBINED GAS LAW.

Combining the Gas Laws

V1P1n1T1

V2P2n2T2

OR, if only one set of data exists, a single useful equation results…

The Ideal Gas Laws

When the five minor gas laws are combined, a single useful equation results…

The Ideal Gas Laws

In this equation,

•P should be in atm

•V should be in liters

•n should be in moles

•T should be in Kelvin

•R is the gas constant…

0.0821 atm Lmol K

IGL assumes two things1. molecules have zero volume2. intermolecular attractions are zero

The Ideal Gas Laws