Mr. Shields
Regents Chemistry
U05 L07
P/T = k
(Constant V and n)
Louis Joseph Gay-Lussac (1778 – 1850)
- Gay-Lussac’s Law (abt 1807)
- Pressure vs. Temp relationship
Gay-Lussac Loved Flying
In hot air balloons and made
Ascents to 7000 meters
Gay-Lussac & Biot 1804
Developing GL’s Law
We know from the KMT that The avg. KE of a gas
is directly proportional to Temp. (in Kelvin!)
And since KE = ½ mv2 as Temp increases Molecular
velocity increases
If we hold the volume constant then the frequency of
Molecular collisions with the wall must be increasing
With increasing T since the velocity is increasing.
Developing GL’s Law
If the number of collisions with the wall per unit time
increases then the pressure increases
So as T , vel.
and so does P
Remember T must always be in Kelvin!
Gay-Lussac described this gas behavior as
P/T = k
Since P inc with inc T (and vice versa) this represents
a Direct Relationship between P and T
Developing GL’s Law
You probably noticed that the relationship between
P and T has the same relationship as the one between
V and T
P/T = k
V/T = k
So you might expect a plot of Guy-Lussac’s law to look
The same as Charle’s Law …
And you’ld be right!
A plot of Gay-Lussac’s law
Direct relationship
Notice that Gay-Lussac and Charles law both predict that
P and V go to zero as T goes to -273 deg C.
This temperature is the zero pt. on the Kelvin scale.
Let’s do some problems:
PROBLEM 1: A sample of gas in a container at
30 deg C has a pressure of 1 atm. If the temperature
is increased to 200 deg. Celsius, at constant V and n,
what pressure will the gas have?
P1/T1 = P2/T2
1 atm / 303K = P2 / 473 deg K
P2 = (1 x 473)/303
P = 1.56 atm
Problem 2
A fire broke out in a nitrogen storage facility. The
Electronic gages on the nitrogen tanks, which at
25 deg C had a normal pressure of 68 atm, recorded
the Highest pressure the tanks were subjected to was
285 atm. What was the temperature of the fire in the
Nitrogen storage room in Kelvin and deg. C?
P1 = P2
T1
T2
T2 = 1249 K
T2 = 976 C
68 atm
298K
=
285
T2
(or 1,788 deg. F)