Chapter 14 Notes Part I Boyle’s, Charles’ and Gay- Lussac’s Laws Combined Gas Laws

In Chapter 13 gases were said to be mostly empty space.In Chapter 13 gases were said to be mostly empty space. This gives rise to a property called compressibility.This gives rise to a property called compressibility. The particles in a gas can be forced closer together.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.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: as the volume of a gas is ↓, the amount of pressure is ↑ at a constant temperature.Boyles Law: as the volume of a gas is ↓, the amount of pressure is ↑ at a constant temperature. –(P  V  or P  V  ) –Mathematically, P 1 V 1 = P 2 V 2

Why? With less volume, there is greater frequency of the same amount of particles hitting the 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=°C+273

Charles Law: as the temperature of a gas ↑, the volume is also ↑ at constant pressure. –(V  T  or V  T  ) –Mathematically: V 1 = V 2 T 1 T 2

Why? As the temperature, the average kinetic energy of the particles.As the temperature ↑, the average kinetic energy of the particles ↑. This the amount of volume needed to maintain the same frequency of collision with the surface of the container.This ↑ the amount of volume needed to maintain the same frequency of collision with the surface of the container.

Practice Problem #2 A balloon has a volume of 6.7L at 20 o C. What will its volume be at 350 o C 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. –(P  T  or P  T  ) –Mathematically: P 1 = P 2 T 1 T 2

Why? As the temperature, the average kinetic energy of the particles, thus they move faster.As the temperature ↑, the average kinetic energy of the particles ↑, thus they move faster. This increases the frequency of collisions, as well as the amount of force in each collision.This increases the frequency of collisions, as well as the amount of force in each collision.

Practice Problem #3 The pressure in an automobile tire that has a constant volume is 198 kPa at 27 o C. 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 P 1 V 1 P 2 V 2 T 1 T 2 =

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 25 o C 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 125 o C. What is the new volume?A gas at 155 kPa and 25 o C 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 125 o C. What is the new volume?