Gas laws

1. Gay-Lussac’s Law
(And a few
other topics.)

2. Gay-Lussac was a balloonist.
Gay-Lussac (1778-1850)
In 1802 he went up to 23,000 feet in a
balloon – a record for 50 years.
Wanted to investigate the composition of
the atmosphere as a function of altitude.

3. Gay-Lussac
Examined relationship betw P & T at
constant V and moles
If T , the gas molecules will move faster,
colliding with the walls more frequently &
more energetically.
Pressure results from collisions between
gas molecules & walls of container. So, if
T , we expect P .

4. Gay-Lussac
Tiger Graphic

5. Which
temperature
scale has a
direct
relationship to
molecular
velocity?
Kelvin

6. k
T
P

P
T
C. Gay-Lussac’s Law
Temperature
(K)
Pressure
(torr)
P/T
(torr/K)
248 691.6 2.79
273 760.0 2.78
298 828.4 2.78
373 1,041.2 2.79

7. k
T
P

P
T
C. Gay-Lussac’s Law
The pressure and absolute
temperature (K) of a gas are
directly related
– at constant mass & volume

8. Typical data from a Gay-Lussac type experiment.
What kind of relationship is illustrated in this graph?
T (K)

9. Gay-Lussac’s Law
Describes relationship between pressure &
temperature at constant volume & amount.
P = kT or P/T = k
What kind of relationship is this?
Straight line with y-intercept of zero. It’s
direct.

10. Gay-Lussac: Verbal
The pressure exerted by a confined gas is
directly related to the Kelvin temperature
at constant volume.

12. When temperature decreases, the
pressure of a gas (decreases, increases,
stays the same).
When temperature increases, the pressure
of a gas (decreases, increases, stays the
same).
Decreases
Increases

13. Gay-Lussac’s Law
P1 = P2
T1 T2
Useful problem-solving format.

14. GIVEN:
P1 = 765 torr
T1 = 23°C = 296K
P2 = 560. torr
T2 = ?
WORK:
P1V1T2 = P2V2T1
E. Gas Law Problems
A gas’ pressure is 765 torr at 23°C. At
what temperature will the pressure be
560. torr?
GAY-LUSSAC’S LAW
P T
(765 torr)T2 = (560. torr)(296K)
T2 = 217 K = -56.3°C