The Nature of Gases

ChemistryK. Culbertson

Gases Occupy Space• All matter, including gases, have

mass and occupy space• Paper demo• Balloon in a bottle demo

Gases Occupy Space• Paper demo

• The air trapped in the container occupied volume and prevented water from entering

• Balloon in a Bottle• The air/gas in the bottle is compressed.

The compressed air exerts more pressure on the balloon than even the largest student can blow into it.

Kinetic Theory• Tiny particles in all forms of

matter are in constant motion

Kinetic Theory

• Particles in motion exert forces when they collide with other bodies

•Gas pressure is the result of simultaneous collisions of tons of gas particles with an object

Effective collision

Ineffective collision

Kinetic Theory• Balloon Demonstration

• Explain the process of blowing up the balloon in terms of gas particles

• Explain why the balloon blows up using the kinetic theory

Kinetic Theory• Balloon Demonstration:

• Gas (Carbon Dioxide) from the lungs is blown into the balloon• You are increasing the number of gas

particles in the balloon• The gas particles are in constant

motion and exert a force or pressure on the inside wall of the balloon causing it to expand

Atmospheric Pressure• Air exerts pressure on Earth

because gravity holds air molecules in Earth’s atmosphere

• Atmospheric pressure refers to the collisions of air molecules with objects

Atmospheric Pressure• The air around you exerts pressure

on your body all the time. Can you feel it?

Atmospheric Pressure• If you have the same pressure

both inside and outside (atmospheric pressure) of an object then the forces created by those objects are equal• The object will not be crushed or

expand

Mauna Kea

Atmospheric Pressure• The pressure inside

the balloon must have been _______ the pressure on the outside of the balloon (atmospheric pressure) for the balloon to expand.

The Collapsing Can:• Procedure:

• Fill a can with 10-12mL of water• Fill a pan with cold water• Heat the can over a Bunsen burner

until water is boiling and steam is visible

• Invert the can in the cold water making sure that the opening is completely submersed

The Collapsing Can:• What happened?

The Collapsing Can:• Demonstrates:

• The effect of atmospheric pressure (pressure of the gases in the air) on an object

• The effect of temperature on a gas

Effect of Increasing Temperature on Gases• Heating the water in the can

• Increasing the temperature of the liquid water caused the liquid to become water vapor

• Increasing the temperature speeds up the particles

• Increasing the speed means more collisions against the object

• Increases the pressure inside the object

Effect of Increasing Temperature on Gases• When you increase the

temperature you ___________ the pressure

• Why didn’t the can expand because of increased pressure?

Effect of Decreasing Temperature on Gases• What was the effect of putting the

can in cold water?• Seals the top of the can• Decreasing the temperature

decreases the speed of the gas particles• Gas particles condense

• Causes a pressure difference between the atmosphere and inside the can

Standard Temperature• 0ºC or 273K• Celsius to Kelvin

• ºC + 273 = Kelvin• Kelvin to Celsius

• Kelvin - 273 = ºC

Standard Pressure• 101.3 kPa (kilopascals) or 1atm• Convert atm to kPa

1 atm101.3 kPaxG atm

101.3 kPa1 atmxG kPa

Variables used to describe a gas1. Pressure (kPa)2. Volume (L)3. Temperature (K)4. n (number of moles)

** Our goal is to be able to predict the behavior of a gas given specific conditions