Gay-Lussac's Law
Joseph-Louis Gay-Lussac
In the early 1800’s, Gay-Lussac
ascended to a height of
approximately 23,000 ft in a hot
air balloon to study variations in
the Earth's electro-magnetic
intensity relative to altitude. On
this flight, he experienced the
effects of oxygen deprivation but
still managed to collect air
samples at over 20,000 ft, study
the variation of pressure and
temperature, and continue his
observations on electromagnetism.
What is Gay-Lussac’s Law?
Gay-Lussac's Law states
that the pressure of a
sample of gas at constant
volume, is directly
proportional to its
temperature in Kelvin.
Mathematically Gay-Lussac’s Law can be
expressed as P1 = P2
T1 T2
P1 T2 = P2 T1
•
•
•
•
P1 is the initial pressure
T1 is the initial temperature (in Kelvin)
P2 is the final pressure
T2 is the final temperature (in Kelvin)
Gay-Lussacs’s Law Practice
Problems
1. A tank of gas has a pressure of 2.75 atm
at 20°C. What will be the new pressure
in the tank if its temperature is increased
to 100°C?
P1 T2 = P2 T1
P1:
T1:
P2:
T2:
2. A gas system has initial pressure of 793
kPa and temperature of 34.5°C If the
pressure changes to 446 kPa, what will the
resultant temperature be in K?
P1 T2 = P2 T1
P1:
T1:
P2:
T2:
COMBINED GAS LAW
The combined gas law is a combination of
Boyle's Law and Charles's Law; hence its
name the combined gas law. In the
combined gas law, the volume of gas is
directly proportional to the absolute
temperature and inversely proportional to
the pressure.
Mathematically, Combined Gas Law
can be expressed as P1V1 = P2V2
T1
T2
•
•
•
•
•
•
P1V1 T2 =P2V2 T1
P1 is the initial pressure
V1 is the initial volume
T1 is the initial temperature (in Kelvin)
P2 is the final pressure
V2 is the final volume
T2 is the final temperature (in Kelvin)
Combined Gas Law Practice
Problems
1. A sample of gas occupies a volume of 75 mL at
a pressure of 725 mmHg and a temperature of
18°C. What volume would this sample of gas
occupy at 800 mmHg and 298K?
P1V1 T2 =P2V2 T1
P1:
V1:
T1:
P2:
V2:
T:
2. A sample of gas occupies a volume of
3.75 L at a pressure of 1.15 atm and a
temperature of 25°C. At what
temperature will the sample of gas
occupy 4 L at a pressure of 1 atm?
P1V1 T2 =P2V2 T1
P1:
V1:
T1:
P2:
V2:
T2: