9.1 Pressure and Kinetic Molecular Theory of Gases

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Properties of Gases

Gases have no definite shape or volume.

(Liquids have a definite volume but no definite shape. Solids have definite shape and volume.)


Pressure = Force / Area          P = F / A          SI Unit is the Pascal


1atm = 760torr = 760mmHg = 101,325Pa = 101.325kPa

Kinetic Molecular Theory (Ideal Gas Theory)
1 Gas atoms/molecules occupy negligible volume compared to the space between atoms/molecules.
2 Gas molecules don’t experience attractive or repulsive forces between one another.
3 All collisions are elastic (no loss of kinetic energy).
4 A gas is composed of a large number of atoms/molecules in random motion.
5 KEavg α T                (KEavg = 3/2RT)
Ideal Behavior
1. Gases behave more ideally at low Pressure and high Temperature.
2. Gases with less Intermolecular Forces tend to behave more ideally.