1. Due: Gas Laws WS & book problems Today: Ideal Gases Molar Mass of a Gas HW Ideal Gas WS Prep Lab Notebook – Mass of a Volatile Liquid

2. Ideal Gases Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory.  Gases consist of tiny particles that are far apart relative to their size.  Collisions between gas particles and between particles and the walls of the container are elastic collisions  No kinetic energy is lost in elastic collisions

3. Ideal Gas Law PV = nRT R = ideal gas constant n = number of moles use when given moles or grams of a gas Lecture PLUS Timberlake 20003

4. Deriving R – the Gas Law Constant What is the value of R at STP? R = PV = nT Lecture PLUS Timberlake 20004 --

5. Ideal Gas Law Ideal Gas Law PV = nRT P = pressure in atm V = volume in liters n = moles R = proportionality constant = 0.08206 L atm/ mol·  T = temperature in Kelvins Holds closely at P < 1 atm

6. The Ideal Gas Law The ideal gas law allows calculations to be done in which the amount of gas varies as well as the temperature, pressure, and volume.ideal gas law Mathematically, the ideal gas law is written as follows: PV= nRT In this equation, P, V, and T are the same as in the previous gas laws. The number of moles of gas is represented by n and R is the universal gas constant. A commonly-used value for R is: Given the units of R, what are the units for P, V, and T?

7. Ideal Gas Law Calculations Example 1: A 2.50 mole sample of gas is confined in a 6.17 liter tank at a temperature of 28.0ºC. What is the pressure of the gas in atm? Example 2: A 4.00 g sample of gas is found to exert a pressure of 1.71 atm when confined in a 3.60 L container at a temperature of 27ºC. What is the molecular weight of the gas in grams per mole?

8. Using the Ideal Gas Equation Can be used to find many physical properties of gases Density of a gas Molar Mass of a gas Once this information is found we can use it to determine the VOLUME of a gas formed or used in a Chemical ReactionChemical Reaction

9. Densities of Gases If we divide both sides of the ideal-gas equation by V and by RT, we get nVnV P RT =

10. We know that moles  molecular mass = mass Densities of Gases So multiplying both sides by the molecular mass (  ) gives n   = m P  RT mVmV =

11. Densities of Gases Mass  volume = density So, Note: One only needs to know the molecular mass, the pressure, and the temperature to calculate the density of a gas. P  RT mVmV = d =

12. Molecular Mass We can manipulate the density equation to enable us to find the molecular mass of a gas: Becomes P  RT d = dRT P  =

13. Molar Mass of a gas What is the molar mass of a gas if 0.2664 g of the gas occupy 215 mL at 0.813 atm and 30.0°C? Lecture PLUS Timberlake 200013

14. Real Gases Do Not Behave Ideally Real gases DO experience inter-molecular attractions Real gases DO have volume Real gases DO NOT have elastic collisions

15. Ideal Gas vs. Real gas Lecture PLUS Timberlake 200015