The Behavior of Gases

The Behavior of Gases

Unit 2, Chapter 8, Lesson 3, pg. 291

​Understanding Gas Behavior

​Changes in temperature, pressure, and volume affect the behavior of gases more than they affect solids and liquids.

​​Kinetic Molecular Theory: A set of rules that describe how particles behave in matter.

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1.Small particles make up all matter.

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2. Particles in matter are in constant, random motion.

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3.Particles in matter collide with other particles, other objects, and the walls of their container.

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4.When particles collide, no energy is lost.

Open Ended

How does the kinetic molecular theory describe the differences between gases and solids?

​Pressure

​Pressure: The amount of force applied per unit of area.

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​In gases, as pressure increases, volume decreases.

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​Why?

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​When the particles in a gas are compressed, they have less space to move around. As a result, the particles start to collide with one another more often — this increases pressure!

​Boyle's Law

​Robert Boyle (1627-1691) was a British scientist. He was the first to describe the relationship between volume and gases. He also proved that gases are made up of atoms.

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​Boyle's Law

​P₁V₁ = P₂V₂

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Pressure and Volume have an inverse (opposite) relationship when temperature is held constant.

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The pressure of a gas increases when the volume decreases.

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​The pressure of a gas decreases when the volume increases.

​Boyle's Law in Action

​Air pressure and flying

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​On the ground, your middle ear and the air outside have equal pressure.

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​As the airplane takes off and increases in altitude, the air pressure outside decreases relative to your middle ear.

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​In response to the decrease in pressure, the trapped air in your middle ear increases in volume, which causes pain.

​Graphing Boyle's Law

​Pressure is graphed on the x-axis

​Volume is graphed on the y-axis

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​As pressure increases, volume decreases. This is true only if the temperature of the gas is held constant.

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Draw

Airplanes typically fly at an altitude of about 10 km. At this altitude the atmospheric pressure is significantly less than it is at ground-level. Because of this,

airplane cabins must be pressurized so that the people

on board can continue to get enough oxygen. If a typical

Boeing 747 has a volume of 28,000 m3 and is filled with

air at a pressure of 101.3 kPa on the ground, what is the new volume

of air inside when the cabin is pressurized to 75 kPa once

it is in flight? Did the volume increase or decrease? Use the equation P1V1 = P2V2

​Charles's Law

Open Ended

How is Boyle's law different from Charles's law?

​Charles's Law in Action

Tire Pressure and Charles's Law

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Why do tires "deflate" in the winter?

​Typical manufacturers recommend that automobile tire pressures vary between around 25 to 35 pounds per square inch (PSI). But if you read a car owner's manual carefully, it will mention that tire pressure should always be measured cold. That's because hot weather and driving heat up tires.

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Tire pressure increases because heat increases the amount of space gas particles needs. Since tires don't expand very much, volume stays constant. This increases tire pressure.

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Consequently, measuring tire pressure when the tire is warm will give you the false impression that you have filled your tires with too much air.

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Open Ended

Using what you know about Charles's Law, explain why physical activities like jogging become difficult in freezing winter days.

Hint: Think of your lungs as balloons.

​Graphing Charles's Law

​Temperature is on the x-axis

​Volume is on the y-axis

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• ​Notice how the line in this graph is straight ​

• ​Also, notice how the temperature starts at 0 K.

  • ​0 K is the lowest possible temperature of matter. At absolute zero, particles have no thermal energy.