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.In chapter 10 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. 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.There are three relationships between the conditions a gas is in that will be affected by this property. Pressure and volumePressure and volume Volume and temperatureVolume and temperature Pressure and temperaturePressure 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  )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, Mathematically, P 1 V 1 =P 2 V 2 Robert Boyle

Why? With less volume, there is greater frequency of the same amount of particles hitting the surface of the container.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: V 1 V 2 T 1 T 2 Jaques Charles =

Why? As the temperature increases, the average kinetic energy of the particles increases.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.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: -273 o C!

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

K= o 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) As you increase temperature of an amount of gas, its pressure will increase if at a constant volume. (P  T  or P  T  ) Mathematically: P 1 P 2 T 1 T 2 Joseph Gay- Lussac = 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.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.This increases the frequency of collisions, as well as the amount of force in each collision.

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 #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 20 o C. What will its volume be at 350 o C if it is at constant pressure?

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?

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?