1. AP
Chemistry
The Gas Laws

2. Basics on Gases
composition of the atmosphere:
~78% N2, ~21% O2
properties of gases:
expand to fill container
compressible
form homogeneous mixtures
-- due to gas particles being… 1)
far apart 2)
in constant, random motion
vapors: gases of substances
that are normally
liquids or solids
e.g., gasoline vapors

3. Equation for pressure: F  Nm2
P 
N/m2
= Pa
1 atm…
= 760 mm Hg
= 760 torr
= kPa
= bar
(1 bar = 105 Pa)
At a depth of 350 m (1150 ft),
the hull pressure on a submarine
is 3.4 x 106 Pa (36 tons/ft2).

4. BAROMETER vacuum air pressure mercury (Hg) mercury barometer
Close-up of an early mercury barometer, showing how the mercury column is supported by atmospheric pressure.
BAROMETER
vacuum
air
pressure
mercury (Hg)
mercury
barometer

5. An aneroid barometer contains
a small, pressure-sensitive
metal box that has been
evacuated of air. The box is
prevented from collapsing by
being connected to a spring
that is also attached to the dial
on the barometer. When
the air pressure on the walls
of the box changes, the box
“flexes,” which moves the
spring and the dial.

6. OPEN END MANOMETER
CLOSED END MANOMETER
air pressure
sealed end
confined
gas
Hg height
difference
Pgas = HEIGHT

7. The Gas Laws Boyle’s law: PV = constant (when T is constant)
Robert Boyle
(1627–1691) V V
1/P P

8. Charles’s law: V/T = constant (when P is constant) Jacques Charles V
(1746–1823)
**T in K
(0.00 K = –273.15oC) T

9. Gay-Lussac’s law: P/T = constant (when V is constant) P Joseph Louis
(1778–1850) T

10. Avogadro’s hypothesis: Equal volumes of gas at the
same temperature and
pressure have the same
number of particles.
e.g., 22.4 L of ANY GAS
at STP contains
6.02 x 1023 particles
Amedeo Avocado
Amedeo Avogadro
Avogadro’s law:
(1776–1856)
(1876–1956)
Volume of a gas is
proportional to the
number of moles of gas.
i.e.,

12. Combined Gas law: merges Boyle’s, Charles’s,
and Gay-Lussac’s laws into
one equation.
**NOTE:
For all gas law
calculations, use
the absolute
temperature (in K).

13. Other Equations and Constants
Ideal Gas law:
R = L-kPa/mol-K
= L-atm/mol-K
P V = n R T
Conditions of standard temp. and pressure (STP):
0oC ( K)
1 atm
Equations for gas density:
M = molar mass
of gas
same gas; two
sets of conditions