Lesson 4.5
Gay-Lussac’s and the
Combined Gas Law
I. Gay-Lussac’s Law
•  Jacques Charles showed that raising the
temperature of a gas increases its volume.
•  But what happens if you heat a gas in a
container that cannot expand?
I. Gay-Lussac’s Law
•  Raising temperature  particles move faster
•  Faster particles  more collisions with
container
•  More collisions + fixed volume = ?
•  HIGHER PRESSURE
I. Gay-Lussac’s Law
•  In 1802, Joseph Gay-Lussac determined that
the pressure and temperature of a gas are
directly proportional.
•  P = kT
P1 P2
=
T1 T2
•  Where T is in Kelvin
I. Gay-Lussac’s Law
•  Practice: The gas in an aerosol can is at a
pressure of 3.00 atm at 25°C. Directions on the
can warn the user not to keep the can in a
place where temperature exceeds 52°C. What
would the gas pressure in the can be at 52°C?
•  Hint: K = °C + 273
II. Combined Gas Law
•  What happens when a gas changes
temperature, pressure, and volume…at the
same time!
•  Boyle’s, Charles’, and Gay-Lussac’s Laws can
be combined into a single equation called the
Combined Gas Law.
•  PV = k
T
1 1
2 2
PV P V
=
T1
T2
II. Combined Gas Law
•  Practice: A helium-filled balloon has a volume
of 50.0 L at 25°C and 1.08 atm. What volume
will it have at 0.855 atm 10°C?
•  Hint: K = °C + 273