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.

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)
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$)
 Mathematically,

P1V1=P2V2
Why?

With less volume, there is greater
frequency of the same amount of
particles hitting the surface of the
container.
Temperature and Volume (Charles’
Law)


As the temperature of an amount of gas is increased,
the volume is increased at constant pressure. (V#T#
or V$T$)
Mathematically:
V1 V2
T1 T2
=
Why?
As the temperature increases, the
average kinetic energy of the particles
increases.
 This increases the amount of volume
needed to maintain the same
frequency of collision with the surface
of the container.

Meanwhile...

Jaques Charles also noticed that no
matter what gas he experimented
with, when he extrapolated the
volume down on a graph, the
temperature was the same: -273oC!
Kelvin
William Thomson (a.k.a. Lord Kelvin) recognized
this as the theoretical point at which the average
kinetic energy of all substances would be zero.
 Thus, the concept of absolute zero and the Kelvin
scale were born!

o
K= C+273
When comparing temperatures during this
chapter, they must be in Kelvin, because
Celsius is a degreed scale and Kelvin is an
absolute scale!
Pressure and Temperature (Gay-Lussac’
Law)


As you increase temperature of an amount of gas, its
pressure will increase if at a constant volume. (P#T#
or P$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?
ANS: 6.5L
Practice Problem #2

A balloon has a volume of 6.7L at
20oC. What will its volume be at
350oC?
ANS: 14.2L
Practice Problem #3

The pressure in an automobile tire is
198 kPa at 27oC. On a hot sunny day
the pressure has risen to 225 kPa.
What is the temperature?
ANS: 341K
or 68oC
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?
ANS: 0.34L