Transcript Chapter 4 Notes Boyle’s, Charles’ and Gay-Lussac’s Laws Combined Gas Laws Gases are said to be mostly empty space. This gives rise to a.

Chapter 4 Notes
Boyle’s, Charles’ and Gay-Lussac’s Laws
Combined Gas Laws
Gases are said to be mostly empty
space.
This gives rise to a property called
compressibility.
The particles in a gas can be forced
closer together.
There are three relationships between
the conditions a gas is in that will be
affected by this property.
Pressure and volume
Volume and temperature
Pressure and temperature
Boyles Law states that as the volume of a gas is
decreased, the amount of pressure is increased at
constant temperature.
(P#V$ or P$V#)
Mathematically,
P1V1=P2V2
Why?
With less volume, there is greater
frequency of the same amount of
particles hitting the surface of the
container.
Charles Law states that as the temperature of a gas is
increased, the volume is also increased at constant
pressure.
(V#T# or V$T$)
Mathematically:
V1 = V2
T1 T2
Why?
As the temperature increases, the
average kinetic energy of the
particles increases.
This increases the amount of volume
needed to maintain the same
frequency of collision with the
surface of the container.
Meanwhile...
Jaques Charles also noticed that no
matter what gas he experimented
with, when he extrapolated the
volume down on a graph, the
temperature was the same: -273oC!
Kelvin
William Thomson (a.k.a. Lord Kelvin) recognized
this as the theoretical point at which the average
kinetic energy of all substances would be zero.
Thus, the concept of absolute zero and the Kelvin
scale were born!
o
K= C+273
When comparing temperatures during this
chapter, they must be in Kelvin, because Celsius is
a degreed scale and Kelvin is an absolute scale!
Gay-Lussac’s Law states that as you increase temperature of
an amount of gas, its pressure will increase if at a
constant volume.
(P#T# or P$T$)
Mathematically:
P1 = P2
T1 T2
Why?
As the temperature increases, the average
kinetic energy of the particles increases,
thus they move faster.
This increases the frequency of collisions,
as well as the amount of force in each
collision.
But wait a minute...
Are you saying that I have to keep ALL these
equations straight in my head?
NO! There’s a handy, dandy equation that will show you
ALL these equations in one!
Combined Gas Laws
P1V1 P2V2
=
T1
T2
When one variable is constant, you can just
cross it out, and the equation works for all three
laws, as well as for combined problems!
Practice Problem #1
The pressure on 2.5L of anesthetic gas
changes from 105 kPa to 40.5 kPa.
What will the new volume be if the
temperature is constant?
Practice Problem #2
A balloon has a volume of 6.7L at 20oC.
What will its volume be at 350oC if it
is at constant pressure?
Practice Problem #3
The pressure in an automobile tire that
has a constant volume is 198 kPa at
27oC. On a hot sunny day the pressure
has risen to 225 kPa. What is the
temperature?
Practice Problem #4
A gas at 155 kPa and 25oC occupies a
container with an initial volume of
1.00L. By changing the volume the
pressure of the gas increases to 605 kPa
as the temperature is raised to 125oC.
What is the new volume?