1. Section 13.2 Using Gas Laws to Solve Problems

2. Section 13.2 Using Gas Laws to Solve Problems 1.To understand the ideal gas law and use it in calculations 2.To understand the relationship between the partial and total pressure of a gas mixture 3.To do calculations involving Dalton’s law of partial pressures 4.To understand the molar volume of an ideal gas 5.To learn the definition of STP 6.To do stoichiometry calculations using the ideal gas law Objectives

3. Section 13.2 Using Gas Laws to Solve Problems A. The Ideal Gas Law Boyle’s Law V = k (at constant T and n) P Charles’s Law V = bT (at constant P and n) Avogadro’s Law V = an (at constant T and P) We can combine these equations to get

4. Section 13.2 Using Gas Laws to Solve Problems A. The Ideal Gas Law Rearranging the equation gives the ideal gas law: PV = nRT R is a constant = 0.08206 L atm mol K Note the units that are used with this constant

5. Section 13.2 Using Gas Laws to Solve Problems The Combined Gas Law Ideal Gas Law: PV = nRT P 1 V 1 = nRT 1 or P 1 V 1 /T 1 = nR P 2 V 2 = nRT 2 or P 2 V 2 /T 2 = nR Combined Gas Law: P 1 V 1 /T 1 = P 2 V 2 /T 2 (for a constant number of moles)

6. Section 13.2 Using Gas Laws to Solve Problems What value do we measure for the pressure of a gas as we mix different gases in a container? B. Dalton’s Law of Partial Pressures Dalton’s law of partial pressures For a mixtures of gases in a container, the total pressure exerted is the sum of the partial pressures of the gases present. P total = P 1 + P 2 + P 3 + …….

7. Section 13.2 Using Gas Laws to Solve Problems B. Dalton’s Law of Partial Pressures The pressure is independent of the nature of the particles. The pressure of the gas is affected by the number of particles.

8. Section 13.2 Using Gas Laws to Solve Problems Two crucial things we learn from this are: B. Dalton’s Law of Partial Pressures The volume of the individual particles is not very important The forces among the particles must not be very important

9. Section 13.2 Using Gas Laws to Solve Problems Collecting a gas over water B. Dalton’s Law of Partial Pressures Total pressure is the pressure of the gas + the vapor pressure of the water. Collecting Hydrogen

10. Section 13.2 Using Gas Laws to Solve Problems Collecting a gas over water B. Dalton’s Law of Partial Pressures How can we find the pressure of the gas collected alone?

11. Section 13.2 Using Gas Laws to Solve Problems Molar Volume C. Gas Stoichiometry Molar volume of an ideal gas at STP = 22.4 L Standard temperature and pressure (STP) –0 o C and 1 atm For one mole of a gas at STP, what is the volume?