Gas laws

Kinetic Molecular Theory Particles in an ideal gas… have no volume. have elastic collisions. are in constant, random, straight-line motion. don’t attract or repel each other.

Real Gases Particles in a REAL gas… have their own volume attract each other Gas behavior is most ideal… at low pressures at high temperatures in nonpolar atoms/molecules

Characteristics of Gases Gases expand to fill any container. random motion, no attraction Gases are fluids (like liquids). They flow. CO2 demo no attraction Gases have very low densities. Cats are Fluids: They flow and fill the shape of their container

Characteristics of Gases Gases can be compressed. no volume = lots of empty space Gases undergo diffusion random motion

Characteristics of gases

K = ºC + 273 Temperature ºF ºC K -459 32 212 -273 100 273 373 Always use absolute temperature (Kelvin) when working with gases. ºF ºC K -459 32 212 -273 100 273 373 K = ºC + 273

Pressure Which shoes create the most pressure?

Pressure Barometer measures atmospheric pressure Aneroid Barometer Mercury Barometer Aneroid Barometer

Pressure KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi

Standard Temperature & Pressure STP STP Standard Temperature & Pressure 1 atm 273 K

Boyle’s Law

Boyle’s Law The pressure and volume of a gas are inversely related at constant mass & temp P V P1V1 = P2V2

Practice question If a Helium tank that has an initial volume of 100 mL and a pressure of 5 atm loses 50 mL of Helium what is its new pressure? (5)(100) = P2 (50) 500 = P2 (50) 500/50 = 10 P2 = 10 atm

Charles’ Law

Charles’ Law The volume and absolute temperature (K) of a gas are directly related at constant mass & pressure V T V1 = V2 T1 T2

Practice question If a Helium balloon that has an intial volume of 100 mL and a temperature of 240 K is placed in the sun where it heats to 300 K what is its new volume? (100) = V2 (240) (300) 0.42 = V2 (300) V2 = 125 mL

Gay-Lussac’s Law

P1 = P2 T1 T2 Gay-Lussac’s Law The pressure and absolute temperature (K) of a gas are directly related at constant mass & volume P T P1 = P2 T1 T2

Practice question If a Helium tank that has an initial pressure of 5 atm and a temperature of 240 K is placed in the sun where it heats to 300 K what is the new pressure? (5) = P2 (240) (300) 0.021 = P2 (300) P2 = 6.25 atm

Ptotal = P1 + P2 + ... Dalton’s Law The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases. Ptotal = P1 + P2 + ...

Practice question A scuba tank is filled with a mixture of atmospheric gases. Nitrogen exerts a pressure of 70 atm. Oxygen gas exerts a pressure of 22 atm. Argon exerts a pressure of 4 atm. A fourth gas exerts an unknown amount of pressure. We know the total pressure of the tank is 98 atm. What is the partial pressure of the fourth gas? Ptotal = P1 + P2 + P3 + P4  98 = 70 +22 + 4 + p4 98 = 96 + P4 98-96 = P4 2 = P4

UNIVERSAL GAS CONSTANT Ideal Gas Law PV=nRT UNIVERSAL GAS CONSTANT R=0.0821 Latm/molK R=8.315 dm3kPa/molK

Practice Question How many moles of gas does it take to occupy 120 L at a pressure of 2.3 atm and a temperature of 340 K? PV = nRT  (2.3)(120) = n (0.0821)(340) 276 = n(27.914) 276/(27.914) = n n = 9.89 moles

Gas Stoichiometry Moles  Liters of a Gas STP - use 22.4 L/mol Non-STP - use ideal gas law

Practice question You are given 1 L of carbon monoxide at STP, how many moles of carbon monoxide do you have? 1 L x 1 mol = 0.045 mol carbon monoxide 22.4 L