Transcript Chapter 12 Notes, part I Boyle’s Charles’ and Gay-Lussac’s Laws Combined Gas Laws.

Chapter 12 Notes, part
I
Boyle’s Charles’ and Gay-Lussac’s Laws
Combined Gas Laws
From Last Episode...
• In chapter 10 gases were
said to be mostly empty
space.
• This gives rise to a property
called compressibility.
• The particles in a gas can be
forced closer together.
This guy thinks that compressibility is GROOVY!
3 Relationships...
• 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
Pressure vs. volume (Boyle’s Law)
Robert Boyle
1627-1691
• As the volume of a certain amount of
gas is decreased, the amount of
pressure is increased at constant
temperature. (P#V$ or P$V#)
• Mathematically,
P1V1=P2V2
Why?
• With less volume, there is greater
frequency of the same amount of
particles hitting the surface of the
container.
Temperature and Volume (Charles’
Law)
Jaques Charles
1746-1823
• As the temperature of an amount of gas
is increased, the volume is increased at
constant pressure. (V#T# or V$T$)
• Mathematically:
V1 V2
T1 T2
=
Why?
• As the temperature increases, the
average kinetic energy of the
particles increases.
• This increases the amount of
volume needed to maintain the
same frequency of collision with
the surface of the container.
Meanwhile...
• Jaques Charles also noticed that no
matter what gas he experimented
with, when he extrapolated the
volume down on a graph, the
temperature was the same: -273oC!
Kelvin
• William Thomson (a.k.a. Lord Kelvin)
recognized this as the theoretical point at
which the average kinetic energy of all
substances would be zero.
• Thus, the concept of absolute zero and the
Kelvin scale were born!
Lord Kelvin
1824-1907
o
K= C+273
When comparing temperatures during this
chapter, they must be in Kelvin, because Celsius is
a degreed scale and Kelvin is an absolute scale!
Pressure and Temperature (Gay-Lussac’s
Law)
Joseph GayLussac
1778-1850
• As you increase temperature of an amount
of gas, its pressure will increase if at a
constant volume. (P#T# or P$T$)
• Mathematically:
P1 P2
T1 T2
=
He was also the first person to theorize
that yeast and sugar produces alcohol and carbon dioxide!
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?