The Behavior of Gases Ch. 14 The noble gases walk into a bar. No one reacts. (ba-dum tss!)

When a reaction pauses, Ne is a good sport, he puts his neon the ground

what do you get when you mix sulfur, tungsten, and silver? SWAG

How do you make anti-freeze? Take her nightgown

Did you hear about he guy who chilled himself to absolute zero? He's OK now.

I think I just lost an electron, but I'm not positive.

What does a chemist bring as a dessert while camping? A 'gram' cracker.

What was Avogadro's favorite sport? Golf - because he always got a mole-in-one.

Kinetic Molecular Theory Particles in an ideal gas… –have no volume. –have elastic collisions. –are in constant, random, straight-line motion. –don’t attract or repel each other. –have an avg. KE directly related to Kelvin temperature. Courtesy Christy Johannesson

8 Elastic vs. Inelastic Collisions 8 v1v1 elastic collision inelastic collision POW v2v2 v3v3 v4v4

Kinetic Molecular Theory (KMT) 1.…are so small that they are assumed to have zero volume 2.…are in constant, straight-line motion 3.…experience elastic collisions in which no energy is lost 4.…have no attractive or repulsive forces toward each other 5.…have an average kinetic energy (KE) that is proportional to the absolute temp. of gas (i.e., Kelvin temp.) AS TEMP., KE  explains why gases behave as they do  deals w /“ideal” gas particles…

Combined Gas Law Combined Gas Law = describes the relationship among the pressure, temp., and volume of an enclosed gas – The combined gas law allows you to do calculations for situations in which only the amount of gas is constant – P 1 V 1 /T 1 = P 2 V 2 /T 2 – *SP 14.4, PP pg. 424 I've got a joke you've never xenon here before.

Ideal Gas Law Ideal Gases are gases that conform to the gas laws Ideal Gas Law = the gas law that includes all 4 variables – P, V, T, n – PV=nRT where R is a constant & n is the number of moles Ideal Gas Constant = (R) has the value of 8.31 (L ∙ kPa)/(K ∙ mol) or (atm-L/mol-K) – R = PV/Tn = kPa x 22.4 L/273 K x 1 mol = 8.31 (L ∙ kPa)/(K ∙ mol) *SP 14.5, PP pg. 427 Q: If H 2 O is the formula for water, what is the formula for ice? A: H 2 O cubed

Direct vs. Indirect Charles’ LawPV = nRT Gay-Lussac’s LawPV = nRT Boyles’ LawPV = nRT Direct Indirect

Dalton’s Law Gas pressure results from collisions of particles “” “” depends on # of particles and avg. kinetic energy Partial pressure = the pressure exerted by EACH component of a mixture of gases is the partial pressure of that component In a mixture of gases, the total pressure is the sum of the partial pressures of the gases Dalton’s Law of partial pressures = at constant volume and temp., the total pressure (P T ) exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases – P T = P a + P b + P c + … – *Each diff. gas exerts a diff. pressure SP 14.6, PP pg. 434 Why are chemists so great at solving problems? Answer: Because they have all the solutions.

Dalton’s Law Problems *Suppose you are given four containers – three filled with noble gases. The first 1 L container is filled with argon and exerts a pressure of 2 atm. The second 3 liter container is filled with krypton and has a pressure of 380 mm Hg. The third 0.5 L container is filled with xenon and has a pressure of kPa. If all these gases were transferred into an empty 2 L container…what would be the pressure in the “new” container? *

Mole Fraction where: xixi = mole fraction of any individual gas component in a gas mixture PiPi = partial pressure of any individual gas component in a gas mixture nini = moles of any individual gas component in a gas mixture n= total moles of the gas mixture P= pressure of the gas mixture The mole fraction of an individual gas component in an ideal gas mixture can be expressed in terms of the component's partial pressure or the moles of the component: and the partial pressure of an individual gas component in an ideal gas can be obtained using this expression: The mole fraction of a gas component in a gas mixture is equal to the volumetric fraction of that component in a gas mixture.

41.7 kPa Dalton’s Law of Partial Pressures In a gaseous mixture, a gas’s partial pressure is the one the gas would exert if it were by itself in the container. The mole ratio in a mixture of gases determines each gas’s partial pressure. Total pressure of mixture (3.0 mol He and 4.0 mol Ne) is 97.4 kPa. Find partial pressure of each gas P He = P Ne = 3 mol He 7 mol gas (97.4 kPa) = 55.7 kPa 4 mol Ne 7 mol gas (97.4 kPa) =

Total: 26 mol gas P He = 20 / 26 of total P Ne = 4 / 26 of total P Ar = 2 / 26 of total 80.0 g each of He, Ne, and Ar are in a container. The total pressure is 780 mm Hg. Find each gas’s partial pressure.

More Problems The partial pressure of oxygen was observed to be 156 torr in air with total atmospheric pressure of 743 torr. Calculate the mole fraction of O 2 present. * The mole fraction of nitrogen in the air is Calculate the partial pressure of N2 in air when the atmospheric pressure is 760. torr. *

Graham’s Law Diffusion = tendency of molecules to move towards areas of lower conc. until the conc. is uniform Effusion = the process that occurs when a gas escapes through a tiny hole in its container Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass Graham’s law of effusion = the rate of effusion of a gas is inversely proportional to the square root of the gas’ molar mass

Graham’s Law Problems On average, carbon dioxide travels at 410 m/s at 25 o C. Find the average speed of chlorine at 25 o C. **Hint: Put whatever you’re looking for in the numerator.

At a certain temperature fluorine gas travels at 582 m/s and a noble gas travels at 394 m/s. noble gas What is the noble gas? (582) 2 (394) 2

CH 4 moves 1.58 times faster than which noble gas? Governing relation:

Step 1) Write given information GAS 1 = helium M 1 = 4.0 g v 1 = x GAS 2 = chlorine M 2 = 71.0 g v 2 = x HeCl 2 Step 2) Equation Step 3) Substitute into equation and solve v1v1 v2v2 = 71.0 g 4.0 g Find the relative rate of diffusion of helium and chlorine gas He diffuses 4.21 times faster than Cl 2 Cl He

If fluorine gas diffuses at a rate of 363 m/s at a certain temperature, what is the rate of diffusion of neon gas at the same temperature? Step 1) Write given information GAS 1 = fluorine M 1 = 38.0 g v 1 = 363 m/s GAS 2 = Neon M 2 = g v 2 = x F2F2 Ne Step 2) Equation Step 3) Substitute into equation and solve 363 m/s v2v2 = g 38.0 g 498 m/s Rate of diffusion of Ne = 498 m/s Ne F

Find the molar mass of a gas that diffuses about 4.45 times faster than argon gas. What gas is this? Hydrogen gas: H 2 Step 1) Write given information GAS 1 = unknown M 1 = x g v 1 = 4.45 GAS 2 = Argon M 2 = g v 2 = 1 ?Ar Step 2) Equation Step 3) Substitute into equation and solve = g x g 2.02 g/mol H Ar

Who said chemistry is boring? The following is an actual question given on a University of Washington chemistry mid-term: Q: Is hell exothermic (gives off heat) or endothermic (absorbs heat)? Support your answer with proof. Most of the student wrote proofs of their beliefs using Boyle's Law (gas cools off when it expands and heats up when it is compressed) or some variant answers. One student, however, wrote the following: First we need to know how the mass of hell is changing in time. So, we need to know how the rate that souls are moving into Hell and the rate they are leaving. I thinking that we can safely assume that once a soul gets to hell it will not leave. Therefore no souls are leaving. As for how many souls are entering Hell, let's look at the different religions that exist in the world today. Some of these religions state that if you are not a member of their religion you will go to Hell. Since there are more than one of these religions and since people do not belong to more than one religion, we can project that all people and all souls go to hell. With the birth rates as they are, we can expect the number of souls in Hell to increase exponentially. Now we look at the rate of change of the volume in Hell. Because Boyle's Law states that in order for the temperature and pressure in Hell to stay the same, the volume of Hell has to expand as souls are added. This gives two possibilities. (1) If Hell is expanding at a slower rate than the rate at which souls enter Hell, then the temperature and pressure in Hell will increase until all souls break loose. (2) Of course, if Hell is expanding at a rate faster than the increase of souls In Hell, than the temperature and pressure will drop until Hell freezes over. So which is it? If we accept the postulate given to me by Ms. Theresa Banyan during my freshmen year that "it will be a cold day in Hell before I get with you", and take into account the fact that I still have not succeeded in getting with her, then (2) cannot be true, and this is why I am sure that Hell is exothermic. This student got the only A