Bell Ringer Feb. 22 1) The volume occupied by a sample of gas is 480 mL when the pressure is 115 kPa. What pressure must be applied to the gas to make its volume become 650 mL? 2) The volume of a sample of gas is 2.00 L when the temperature is 11.0 °C. While the pressure remains constant, the temperature is changed to a new value, which causes the volume to become 3.00 L. What was the temperature changed to?

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?

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

Avogadro’s Law - Containers of equal volume have equal numbers of molecules, regardless of the Gas Type. At constant T and P, the volume of a gas increases proportionately as its molar amount increases. If the molar amount is doubled, the volume is doubled.

THE BIG FINALE! IDEAL GAS LAW We will now combine all of the laws that we have learned thus far …. Boyle’s, Charles’, and with Avogadro’s…. Use a Gas Constant (R) 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 = 0.0821 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 0.0821 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 = 0.822 atm 760 mm Hg V = 750 mL x 1 L = 0.750 L 1,000 mL T = 273 + 26 = 299 K R= 0.0821 L * atm n = ? Mol * K

PV = nRT --> rearrange values to solve for n PV = n RT 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 0.822 atm (0.750 L) = n 0.0821 L * atm (299 K) Mol * K 0.025 mol = n

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

Exit Ticket Feb. 22 Dinitrogen monoxide (N2O), 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?