4 Kinetic Model Ideal Gas Assumptions Molecules are spheres2) Molecules identical3) Perfectly elastic collisions(no loss KE).4) No intermolecular forces – constant v between collisions – straight line.5) No molecular volume.
5 Ideal Gasses Obey ideal Gas Law PV = nRTP Pressure PascalsV in m3.n – number of moles.R – gas constant 8.31 J/K mol.T – Kelvin.
6 Pressure Force/Area. Pascal = N/m2. 1 Atm = 101 kPa So if you have 1 m2 window, it has 101,000 N pressing on it.
7 Ex 1: A 360 N child sits on a stool which weighs 41 N Ex 1: A 360 N child sits on a stool which weighs 41 N. The bottom of the stools legs touch the ground over an area of 19.3 cm2:
8 Gas Pressure Gas Molecules Exert Pressure on Container Collisions between gas molecules with each other & the container.Pressure from Dp / impulse of particle = Ft when they bounce & changes p.
9 The Dp (mv) causes impulse, J on walls. F t = J. F = Dp/t is a rate. Low P, less force (KE), lower collision rate.High P, more force (KE), higher collision rate.
12 Temperature Volume T increases, V increases (Fixed P) PV = nRTV = nR TP
13 Temperature & VolumeWhen you push the piston in to reduce the volume, some molecules are swatted giving them E. Work is done on gas.When a gas pushes the piston out, increasing the volume, it does work & the E of the gas goes down.
14 Pressure, Temperature (fixed V) PV = nRTP = nR TV
15 Pressure, TemperatureAs T goes up molecular KE goes up, P goes up. Frequency of collisions go up. Dp increases with Dv. Impulse on wall increases.
17 1. Why does blowing into a balloon increase its volume? 1. Blowing air into the balloon increases the # of air molecules, increasing the rate of collision inside the balloon, and increasing the pressure on the balloon wall.
18 Particulate Nature of Matter and Changes of State 4 min. https://www.youtube.com/watch?v=ndw9XYA4iF0
19 Homework: Read Hamper Chap 3. 3. Look at purple box pg 62 Homework: Read Hamper Chap 3.3. Look at purple box pg 62. For each assessment statement – write a few sentences to address the learning goal. In Class finish IB packet in groups.
22 Pressure Calc’sEx 1. A 360 N child sits on a three legged stool which weighs 41 N. The bottom of the stools legs touch the ground over an area of 19.3 cm2.What is the average pressure exerted by the stool on the ground? (hint: change cm2 to m2)How does the pressure change the student balances the stool on two legs?
32 How do we account for the mass or the amount of substance present?
33 Avogadro's Law If temperature and pressure remain constant... What would happen to the volume of a gas if thenumber of moles (amount of molecules) is increased?
34 Effect of changing mass (# moles) on volume Effect of changing mass (# moles) on volume. Density ratio of mass to volume is constant. Direct Relationship.
35 What would happen to pressure of a gas as mass/moles increased?
36 Pressure vs Mass is direct Pressure vs Mass is direct. The density (mass/volume) increases as the volume is held fixed by the piston and the temperature is fixed.
37 The mass changed by injecting molecules The mass changed by injecting molecules. The density (mass/volume) changes with the injection of the mass. This would be a very difficult experiment to perform in reality, because both P and V must be held constant.
38 Avogadro: Equal volumes of gas at STP have equal #of molecules. Mole is an amount.At STP 1 mol has Avogadro’s number NA of particles (atoms or molecules).NA = 6.02 x 1023 molc/mol.
39 To find # moles, n, in substance given the mass of substance. n = m m = mass in gM M = molar mass #g/molfrom periodic table.1 mole of any gas has fixed volume.At STP the volume is 22.4 dm3 or 22.4 L.
41 Using the ideal Gas LawEx: A weather balloon volume 1.0 m3 contains helium at a pressure of 1.01 x 105 N/m2 and a temperature of 35oC. What is the mass of the helium in the balloon if one mole of helium has a mass of x 10-3 kg?