Gas Laws
Properties of gases
Gases always fill their containers.
 Gases are highly compressible.
 Gases diffuse and mix.
 Temperature affects volume or pressure
of a gas, or both.

Empirical definition

A gas is a substance that fills and
assumes the shape of its container,
diffuses rapidly and mixes with other
gases.
Pressure

Pressure is force
per unit area.
Pressure
Pressure Units
The SI unit for pressure is the kilopascal
(kPa): a force of 1000 N on 1 m2.
 At sea level the average atmospheric
pressure is about 101 kPa. One
standard atmosphere (1 atm) is defined
as 101.325 kPa.

Pressure units
1 bar = 100 kPa
 1 atm = 760 mm of Hg
 1 torr = 760 mm of Hg

Barometer
Standard values
SATP: standard ambient temperature
and pressure is defined as 25°C and
100 kPa.
 STP: standard temperature and
pressure is defined as 0°C and 101.325
kPa.

Boyle’s Law

The relationship between gas pressure
and volume is an inverse relationship.
v α 1
p
Boyle’s Law equation
p1v1 = p2 v2
Assumes temperature is constant.
Example

A 4.57 L volume of gas at SATP is
compressed to 1.67 L. Find the
pressure of the compressed gas.
Solution
p1v1 = p2 v2
Recall: at SATP pressure is 100 kPa
100 kPa • 4.57 L = p2 • 1.67 L
p2 = 273.6526… kPa
p2 = 274 kPa
Your turn
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