Chapter 14 Notes Chapter 14 Notes Part IPart I

Boyle’s, Charles’ and Boyle’s, Charles’ and Gay-Lussac’s LawsGay-Lussac’s Laws

Combined Gas LawsCombined Gas Laws

• In Chapter 13 gases were said to be In Chapter 13 gases were said to be mostly mostly empty spaceempty space..

• This gives rise to a property called This gives rise to a property called compressibilitycompressibility..

• The particles in a gas can be forced The particles in a gas can be forced closer together.closer together.

• There are three relationships There are three relationships between the conditions a gas is in between the conditions a gas is in that will be affected by this property.that will be affected by this property.– Pressure and volumePressure and volume

– Volume and temperatureVolume and temperature

– Pressure and temperaturePressure and temperature

•Boyles Law:Boyles Law: as the volume of as the volume of a gas is ↓, the amount of a gas is ↓, the amount of

pressure is ↑ at a pressure is ↑ at a constant constant temperaturetemperature. .

– (P(PVV or P or PVV))

– Mathematically, Mathematically, P1V1 = P2V2

Why?

With less volume, there is greater frequency With less volume, there is greater frequency of the same amount of particles hitting the of the same amount of particles hitting the

surface of the container.surface of the container.

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?

Note: When comparing temperatures during this chapter, they must be in Kelvin,

because Celsius is a degreed scale and

Kelvin is an absolute scale!

K=K=°°C+273C+273

•Charles Law: as the temperature of a gas ↑, the volume is also ↑ at

constant pressure.

– (VT or VT)

–Mathematically:V1 = V2

T1 T2

Why?• As the temperature As the temperature ↑, the average , the average

kinetic energy of the particles kinetic energy of the particles ↑..

• This This ↑ the amount of volume needed the amount of volume needed to maintain the same frequency of to maintain the same frequency of

collision with the surface of the collision with the surface of the container.container.

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?

• Gay-Lussac’s Law: as you ↑ temperature of an amount of gas, its pressure will ↑ if at a constant

volume.

– (PT or PT)

–Mathematically:P1 = P2

T1 T2

Why?• As the temperature As the temperature ↑, the average , the average kinetic energy of the particles kinetic energy of the particles ↑, thus , thus

they move faster.they move faster.

• This increases the frequency of This increases the frequency of collisions, as well as the amount of collisions, as well as the amount of

force in each collisionforce in each collision..

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?

But wait a minute...

NO! There’s a handy, dandy equation that will show you ALL these equations in one!

Are you saying that I have to keep ALL these equations straight in my head?

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 #4• A gas at 155 kPa and 25A gas at 155 kPa and 25ooC occupies a C occupies a

container with an initial volume of container with an initial volume of 1.00L. By changing the volume the 1.00L. By changing the volume the pressure of the gas increases to 605 pressure of the gas increases to 605 kPa as the temperature is raised to kPa as the temperature is raised to 125125ooC. What is the new volume?C. What is the new volume?