Gases Kinetic-Molecular Theory of Gases Notes#5

§All particles are in constant motion. §As temperature increases kinetic energy ? increases §As gas particles move apart the volume ? increases

Point Masses §Gas particles are treated as a point with no volume and no mutual attraction -this is because they’re so small compared to the distances between them.

Ideal Gases §A theoretical gas with no volume and no attraction. §A series of theories will be studied about ideal gases -standard pressure of kPa -standard temperature of 0°C or 273K -standard conditions are abbreviated STP

Therefore: §Kinetic theory explains properties of gases based on a molecular view. §The assumptions are: l The molecules are in continuous, random motion. l A molecule has negligible volume. l The forces between molecules are negligible. l The average kinetic energy depends on the temperature.

Four Gas Law Variables Are: §V = volume §P = pressure §T = temperature §n = number of particles §(Case is important)

Behavior of Gases §Compression §Expansion §Diffusion – movement of material from high to low concentration - lighter particles diffuse faster than heavier particles §Effusion- gas escapes through a tiny opening

Gas Pressure §Pressure = force/area §Snowshoes in the snow – force is spread out over a larger area §Gas particles exert pressure as they collide with the walls of their container §More particles in a given space, greater pressure §Barometer is tool used to measure atmospheric pressure – mercury rises or falls

Units of pressure §SI unit is Pascal (Pa) §1Pa = 1 N/m 2 derived from force §1atm = 760mm Hg = 760 torr = kPa =14.7 psi §1torr = 1 mm Hg

Dalton’s Law of Partial Pressure §Total pressure of a mixture of gases is equal to the sum of all the pressures of the individual gases §Pg. 392 practice problems

Boyle’s Law §Relates volume and pressure -gas exerts pressure on its container’s walls -pressure depends on *number of molecules *average kinetic energy of the molecules §Pressure = P

Boyle’s Law §Relates volume and pressure -gas exerts pressure on its container’s walls -pressure depends on *number of molecules *average kinetic energy of the molecules §Plunger applies pressure (now 2P). -As pressure doubles, volume becomes ½. -(note the same number of particles now occupying ½ the space)

Boyle’s Law §Boyle’s Law PV=k *P=pressure *V= volume *k=constant §Experiments happen at room temperature(about 25ºC.) We need to convert the results to STP.

Boyle’s Law §Sinceand §then (substituting for k)

Boyle’s Law §Sinceand §then (substituting for k) or

Boyle’s Law §Sinceand §then (substituting for k) or §Units l pressure - kPa l volume - cm 3

Problem: a gas is collected in a 242 cm 3 container at 87.6 kPa. What is its volume at STP? ÀV 1 = P 1 =V 2 = P 2 = ÁThink: pressure goes from 87.6 kPa to kPa so Volume should be________ than 242 cm 3 ÂMath: kPa242 cm kPa?

§so §Note: 209 < 242cm 3 §Now do CMC 358: 1, 2, 3(a,c,e) and 4(a,c,e).