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 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 volume ie – volume goes down, pressure goes up!

BOYLE’S LAW EQUATION P 1 V 1 =P 2 V 2 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 V 2 = (P 1 V 1 ) / P 2 = (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 to Temperature 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 C. At what temperature will the gas occupy a volume of 1.54 L if the pressure remains constant? V 1 = 3.20 L T 1 = K V 2 = 1.54 L T 2 = ? T 2 = V 2 x T 1 V1V L x K 3.20 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 K if its original volume was L at atm and K?