Transcript The Gas Laws - Baker High School

The Gas Laws
1.Boyle’s Law
2.Charles’ Law
3.Gay-Lussac’s Law
4.Avogadro’s Law
Boyle’s Law
Boyle’s Law – at constant temperature, the
volume of the gas increases as the pressure
decreases. The volume of the gas decreases and
the pressure increases.
V↑ P↓
V
o
l
u
m
e
L
P1V1 = P2V2
If you squeeze a
gas sample, you
make its volume
smaller.
Pressure (kPa)
Now . . . a
container where
the volume can
change (syringe)
Moveable
piston
↕
Same
temperature
Volume is 100 mL at
25°C
Volume is 50 mL at
25°C
In which system is the pressure higher? (Which has the greater number
of collisions with the walls and each other?)
Charles’ Law
Charles’ Law – at a constant pressure, the
volume of a gas increases as the temperature of the
gas increases and the volume decreases when the
temperature decreases.
• increase AKE
• increase the speed of
the particles
• the walls of a flexible
container expand –
think of hot air balloons!
V
o
l
u
m
e
V1
V2
=
T1
T2
L
Temperature (K)
Steel cylinder (2L)
contains 500
molecules of O2 at
400 K
Steel cylinder (2L)
contains 500
molecules of O2 at
800 K
1. In which system do the O2 molecules have the highest average kinetic
B
energy?
2. In which system will the particles collide with the container walls with the
B
greatest force?
3. In which system is the pressure higher?
B
Gay-Lussac’s Law
Gay-Lussac’s Law – the pressure of a gas is
directly proportional to its absolute temperature at
a constant volume.
P1 = P2
T1
T2
Pressure
(atm)
Temperature (K)
To remember how these work. . .
PTV
Think “Public Tele Vision”
To remember which constants go
with which law . . .
Boyle’s Law – Temperature is constant
BLT
Charles’ Law – Pressure is constant Cheese Pizza
Gay-Lussac’s Law – Volume is constant
Green
Veggies
Combined Gas Law
P1V1 = P2V2
T1
T2
The equation is found on Table T.
Note that all temperatures must be in
Kelvin!
Units used to describe gas samples:
Volume
Liter (L)
Milliliter (mL)
1000 mL = 1L
Temperature
Kelvin ONLY
Pressure
Atmosphere (atm)
Kilopascale (kPa)
1 atm = 101.3 kPa
1 atm = 760 mm Hg
1 atm = 760 torr
Avogadro’s Law
Avogadro’s Law – equal volumes of gases
at the same temperature and pressure
contain equal numbers of molecules.
H2
O2
CO2
1 mole of ANY gas takes up a volume of
22.4 L at STP.

YouTube - Chemistry Music Video 7: Rock
Me Avogadro
Ideal Gases
• Gases whose behavior can be predicted
by the kinetic molecular theory are called
ideal, or perfect, gases. No gases are
truly ideal because no gas totally obeys all
of the gas laws.
• An ideal gas is an imaginary gas that is
perfect and does follow everything
perfectly.
Ideal Gases, continued
An ideal gas does not condense to a
liquid at low temperatures
 An ideal gas does not have forces of
attraction or repulsion between
particles
 An ideal gas is composed of particles
that have no volume.

Real Gas Vs. Ideal Gas
 A real
gas is most like an ideal
gas when the real gas is at a low
pressure and a high temperature.
 The gases that act most like ideal
gases are the small mass ones –
hydrogen and helium.
Diffusion
• movement
of particles from areas of high
concentrations to areas of low concentration.
•Gases diffuse and mix with other gases very rapidly
due to their rapid motion. (Think ammonia, tuna or
skunk smell.)
•It eventually reaches equilibrium and the mixture is
homogeneous.
Entropy is the randomness of particles.
Effusion – the passage of gas under pressure
through a small opening. (Gases effuse through
a hole in your tire!)
Two More Laws!!
Graham’s Law – Particles of low molar mass travel
faster than heavier particles.
Hydrogen effuses 4 times faster than oxygen.
Dalton’s Law of Partial Pressure In a mixture of gases, each gas exerts a certain pressure
as if it were alone. The pressure of each one of these
gases is called the partial pressure. The total pressure of
a mixture of gases is the sum of all of the partial
pressures.
Ptotal = PA + PB + PC
Example:
A closed cylinder contains 3L of He, 1L of H2
and the total pressure in the system is 800 torr.
What is the partial pressure of the He?
Ptotal = PA + PB + PC
3L + 1L = 4L
4L = 800 torr
4
4
→
1L H2
3L He
4L gas
200 torr
600 torr
800 torr
AND
4L = 800 torr
1L = 200 torr

YouTube - MythBusters - Fun With Gas