Gases

Kinetic Energy and Temperature

Temperature

• We have to measure temperature of gases in Kelvin

• Gases below 0°C are still gases and have kinetic energy

• Kelvin = Celsius temperature + 273

• Equations involving gases include moles or grams – using a temperature like -5°C might result in negative mass!

• 0 Kelvin means no kinetic energy– No motion– Absolute Zero

Diffusion of Gases

BOYLE’S LAW

VOLUME AND PRESSURE

What happened to the helium balloon you lost when you were a kid?

ROBERT BOYLE ~1620

Pressure of a gas is inversely proportional

to its volumeie – volume goes

down, pressure goes up!

BOYLE’S LAW EQUATION

• P1V1=P2V2

• Suppose a helium balloon had a volume of 2L at 1.0 atm. How big would the balloon become if the pressure was reduced to 0.2 atm?

• Solve for V2

• = (P1V1) / P2

• = (1 x 2)/0.2 = 10.0L

• Could a balloon stretch to this volume?

Barometric Pressure

How do you measure pressure?

• Pounds per square inch – psi• Bars and millibars• mm of Mercury• Inches of Mercury• Torrichelli (Torr = 1 mm Hg)• Atmospheres (Atm)• Pascals (P)

• 760mm Hg = 760 Torr = 1 atm = 101,325 P • 1 bar = 100,000 P• 25.4 mm Hg = 1 inch Hg

Effect of Temperature on Volume(Charles’ Law)

Low Temperature High Temperature

The volume of a gas increases with an increase in temperature.

As T increases, V Increases

Always use Temperature in

Kelvin!

Why?Kinetic theory of gases

• Average kinetic energy is proportional toTemperature

• When Temperature is increased, gas molecules hit walls with greater Force, which increases the pressure

• BUT if we want keep the pressure constant, volume must increase to return the pressure to normal

• SO increasing Temperature, increases Volume

A sample of gas occupies 3.20 L at 125 0C. At what temperature will the gas occupy a volume of 1.54 L if the pressure remains constant?

V1 = 3.20 L

T1 = 398.15 K

V2 = 1.54 L

T2 = ?

T2 = V2 x T1

V1

1.54 L x 398.15 K3.20 L

= = 192 K

• Pressure of a gas in a container

• Temp (K) of a gas

• Volume of a gas

• All influence each other

When some property of a gas changes…

• Combined Gas Law

• If one property stays constant, it cancels out!

Example

• What is the volume of gas at 2.00 atm and 200.0 K if its original volume was 300.0 L at 0.250 atm and 400.0 K?