Gas 3 Kinetic Molecular Theory Real vs Ideal Ideal Gas Law

Real Gases KMT is for Ideal Gases only. Real Gas—gas that doesn’t behave ideally under all conditions. –Must take into account space between molecules and attractive and repulsive forces. RULE: The bigger the gas and the closer it is to being a liquid, the less ideal it is. –Ex: CO 2 less ideal than O 2 link

Let’s Combine These Laws….again Gay-Lussac: P=Tg Boyle’s: V=b/P Charles’s: V=cT Avogadro’s: V=an R is the universal gas constant.

Ideal Gas Law Why so many values for R? Units! PV=nRT, solve for R R=PV/nT The units of R must “cancel out” the rest of the units

PV=nRT Ideal Gas Law If gases follow the Kinetic Molecular Theory, they are said to be ideal gases. Although there is no such thing as an ideal gas, the theory still provides a good model to explain gas properties (P,V, T)

Van der Waals Equation a & b are constants –Unique to every gas –Must be given NOTE: Press for real gases are higher & Vol are lower Real Gases

PV=nRT Our mascot has a volume of 2.34L, and he’s at 22.5°C, at 98.2kPa. How many moles of Helium does he contain? P=98.2kPa V=2.34L n=? R= T=295.5K =0.0935mol How do I know which R to use? kPaL/molK

PV=nRT A sample of H 2 gas has a volume of 8.56L at a temperature of 273K (we still need temperature in K) and a pressure of 1.5atm. Calculate the number of moles (n) present in the gas sample. P=1.5atm V=8.56L n=? R= atmL/molK T=273K =0.57mol Which R value do I use?

Ideal Gas Law has its uses PV=nRT Density= mass/volume –D=m/V Molar mass = mass/mole –MW=m/n Rearrange and substitute as necessary to solve for the following Density of a gas given Molar mass of a gas

Ideal Gas Law has its uses PV=nRT Density= mass/volume –D=m/V Molar mass = mass/mole –MW=m/n MW=m/(PV/RT) = mRT/PV MW=DRT/P=DV/n D=MWP/RT= MWn/V D=m/(nRT/P) = mP/nRT