The Behavior of Gases

​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.

​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!

​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.

​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.

​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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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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​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.