IDEAL GAS LAW & Avogadro’s Law What is the IDEAL GAS LAW? What are the variables involved? What is Avogadro’s Law and didn’t I already learn about him with the mole?

Avogadro’s Law l Avogadro’s Law - used to compare number of particles of gases l States that at constant temperature and pressure, the volume is directly proportional to the number of moles of gas Volume and amount of gas (# of moles, n) are directly proportional V α n Amedeo Avogadro

Avogadro’s Law - Containers of equal volume have equal numbers of molecules, regardless of the Gas Type.

THE BIG FINALE! IDEAL GAS LAW l We will now combine all of the laws that we have learned thus far …. Boyle’s, Charle’s, Gay-Lussac’s, with Avogadro’s…. l Use a Gas Constant (R) l AND RESULT WITH ONE FINAL EQUATION THAT RELATES T, P, V, n,

What is R ? - R is called the Ideal Gas Constant or Universal Gas Constant - Instead of learning a variety of values of R for all the possible unit combinations, we memorize one value and convert the units R = L * atm Mol * K - Derived from the fact that one mole of gas at STP occupies 22.4 L

Using PV=nRT P = Pressure (atm) V= Volume (L) T = Temperature (K) n = number of moles R = gas constant L * atm Mol * K ** ALL DATA MUST BE IN PROPER UNITS ** - Always check your units as you set up your equation!

Practice Problem PV=nRT EX. How many moles of N2 are in a 750 mL vessel at 26 degrees Celsius and 625 mm Hg? Step 1 : Convert knowns to correct units so we can use R. P = 625 mm Hg x 1 atm = atm 760 mm Hg V = 750 mL x 1 L = L 1,000 mL T = = 299 K R= L * atm n = ? Mol * K

EX. How many moles of N2 are in a 750 mL vessel at 26 degrees Celsius and 625 mm Hg? Step 2: Plug in values and solve for unknown. PV = nRT --> rearrange values to solve for n PV = n RT atm (0.750 L) = n L * atm (299 K) Mol * K mol = n

Deviations from IDEAL Gas Law l Remember- Real gases deviate from ideal behavior at: LOW Temp and HIGH Pressure REAL gas molecules have volume REAL gas molecules have intermolecular forces

More Practice Dinitrogen monoxide (N 2 O), laughing gas, is used by dentists. If 2.86 mol of gas occupies a 20.0 L tank at 23 degrees Celsius, what is the pressure ( mm Hg) in the tank at the dentists office? How would we tackle this problem?

Don’t forget your concept map! Homework: Finish handout on Ideal Gas Law. Be prepared to ask questions on Monday!