Kinetic Theory and Gases

Objectives Use kinetic theory to understand the concepts of temperature and gas pressure. Be able to use and convert between the Celsius and Kelvin temperature scales.

Kinetic Theory kinetic theory: all matter is made of particles (atoms, ions, molecules) that are in constant, random motion kinetic energy (or KE): the energy of motion; depends on both the mass and speed of the moving particles temperature (T): a measure of the average KE of all the particles in a substance NOT T-E-M-P ! average KE ~ temperature number of particles Kinetic Theory Applet

Kelvin Scale absolute zero: the coldest possible temperature; there is no molecular motion (= -273 o C or 0 Kelvin) K = o C o C = K Kelvin temperature is directly proportional to the KE! 0 K = 0 KE0 o C ≠ 0 KE 600K is 2X more KE than 300K

Objectives Understand the concept of atmospheric pressure. Be able to explain how a barometer works. Be able to convert between pressure measurements.

Gases and Pressure pressure: force applied over an area metric pressure unit: 1 pascal (Pa) = 1 N/m 2 barometer: instrument that measures atmospheric pressure pounds of air push down on each square inch of the earth’s surface (at sea level) spheres DEMO ! Gases exert pressure by collisions.

Pressure Conversions What is the current pressure in kPa and atm? standard pressure (P) = psi = mm Hg = in Hg = kPa = atm standard temperature (T) = 0 o C or 273 K STP: standard T and P

Objectives Be able to use the pressure equation to explain pressure, temperature, and volume changes in gases. Understand how to solve word problems using the “GUESS” method. Be able to use the various gas laws to solve problems.

The Gas Laws Boyle’s Law (constant T) force (F) relates to temperature (T) area (A) relates to volume (V) P and V are inversely proportional Charles’s Law (constant P) P-T Law (constant V) V and T are directly proportional P and T are directly proportional temperature (in K scale) volume

Gas Law Problems Using GUESS Method (1) At constant temperature, 7.5 L of air at 89.6 kPa is compressed to 2.8 L. What is the new pressure? What law was used? (2) A 3.0 L balloon at 22 o C is placed into a freezer at -15 o C. What is the new volume if the pressure remains the same? What law was used? (3) A fixed volume of gas at STP is heated to 482 o C. What is the pressure in kPa at this temperature? What Law was used?

Objectives Understand how the various gas law equations are derived. Be able to use the ideal gas law, gas molar mass equation, and gas density equation to solve problems.

More Gas Laws Combined Gas Law Ideal Gas Law R = 8.31 kPaL/molK n = # moles Gas Molar Mass Gas Density

More Gas Law Problems 1.What is the molar mass of a gas that has a mass of 0.35 g and occupies 165mL at 95 o C and 87.0 kPa? 2.How many moles of air are in a 3.2 L balloon under the current temperature and pressure conditions in this room? 3.What is the density of N 2 gas at 95 kPa and 25 o C?

Objectives Understand Avogadro’s law by considering the ideal gas law. Be able to use the law of combining gas volumes to solve simple gas stoichiometry problems. Be able to use the ideal gas law to solve more complex gas stoichiometry problems.

Avogadro’s Law Avogadro’s Law: equal volumes of gases at the same T and P contain equal numbers of molecules (n) O2O2 HeCO 2 Why? Look at the Ideal Gas Law!

Law of Combining Gas Volumes N 2 (g) + 3H 2 (g) → 2NH 3 (g) Coefficients can represent gas volumes if the reactants and products are at equal T and P. 1 vol. 3 vol. 2 vol. 1 L 3 L 2 L How many liters of H 2 are needed to completely react with 2.5 L N 2 ? Assume same T and P.

Gas Stoichiometry g A → mol A → mol B → g B g A → mol A → mol B → L B (use V = nRT/P) (1) How many liters of CO 2 at 23 o C and 89.5 kPa are formed when a 468 g container of C 3 H 8 is burned? (2) How many liters of H 2 gas are formed when 0.25 g Na reacts with HCl at STP?