Kinetics and Gas Laws

1. Kinetics and Gas Laws Describing states of matter through motion

2. Kinetics: • Kinetics is the study of motion. • Kinetic energy is energy of moving things (potential energy is stored energy) • Two main types of motion: • Vibration: • Translation: • Knowing how particles move can explain how materials behave.

3. Temperature, Heat and Intermolecular forces! • Temperature measures average motion of particles in an object. High temp, particles move fast. • Heat is energy that can be used to move particles. Putting heat into an object can let the particles move faster. • Intermolecular forces hold particles together, the stronger the forces, the more heat needed to make them move.

4. Phase Transitions • It takes energy (heat) to break up a lattice • The bigger the lattice (the more solid you have) the more heat it will take to break the lattice. • We say that the amount of heat to break apart a kilogram of substance is the Heat of Fusion

5. Putting heat into a system • Heat makes atoms move. Kinetics describes motion of atoms • Added heat can go to causing phase changes, or raising temperature • Temperature is a measure of the average kinetic energy of a substance. (i.e. gauges atomic motion)

6. States of Matter • Solids: The Intermolecular forces are strong, and particles can only vibrate,but not translate. • Solids: Fixed Shape and Volume. • Cool any material cold enough (slow down the motion) and they will solidify (freeze). • Things that stay solids even at high temperatures have very strong bonds and intermolecular forces.

7. Solids • Solids are INCOMPRESSIBLE and RIGID • Reason? Crystal Lattice. • Crystal lattice is the pattern that the atoms in a solid are arranged in. • Lattice is like making a pyramid of bottles…

8. The Kinetics of Solids • Motion in solids? Vibration • Think of a cold crowd. Everyone shivers, and maybe the bump into each other a little. • Everyone stays in place (rigid) and you can’t compress a crowd. • What happens when you turn up the heat? • Vibration increases until in breaks the lattice apart…. Think of a mosh-pit.

9. Solid Transitions • Moshing in the Lattice breaks apart the rigid structure. • Going from solid to liquid: Melting • Going from solid to gas: Sublimation • You have to put heat into a solid to break it…. So you have to get heat out to make a solid.

10. Liquids: • In liquids, the particles vibrate, but can also translate somewhat. They slip past each other and flow like a fluid. • Liquids: No fixed shape, what about volume? • Heat most solids, and the molecules will start to translate a bit. • Liquids at room temperature tend to have medium strength intermolecular forces.

11. Liquids • Liquids are difficult to compress, but are not rigid. • Atoms in a liquid vibrate and can translate • Translation: moving from one place to another. • Think of a marathon, a crowd that stays together but can move and jostle for rank.

12. Liquid Crystals • Crystal Lattice • Breaking of lattice in only 1 dimension • Consequences • Uses

13. Liquid Crystals • Some patterns of crystal lattices can break down with heat in one dimension. • Think of a stack of papers… • LCD’s … use liquid crystals to form characters on screens… how? • They use electricity to choose which crystals liquefy and become transparent.

14. Liquid Transitions • Liquids can freeze back to solids. • Add heat to a liquid, and the atoms get enough energy to break away from each other • Results? • Pressure

15. Gases • All translation! Particles run wild. • No fixed shape, no fixed volume. • Weak intermolecular forces. • Gases at room temp need to be cooled to extremely low temperatures to condense (liquefy).

16. Properties of gases • Gases are fluids: fluids are materials that can flow (liquids are also fluids) • Gases are compressible and can diffuse or effuse • We describe gasses with • Pressure • Volume • Temperature • Moles of gas

17. Early gas laws • Boyle’s Law: Keeping the temperature and the amount of gas fixed, the pressure and volume are inversely proportional. • Charles's Law: Keeping the pressure and amount of gas fixed, the volume is directly proportional to the temperature. • Gay-Lussac’s Law: Keeping the volume and amount of gas fixed, the pressure and temperature are directly proportional

18. Dalton’s Law of Partial Pressures • Dalton’s partial pressures: When you have a mixture of gasses, the total pressure of the mix will be equal to the sum of the pressures those gases would have if they were alone in the container.

19. Avagadro’s law of combining volumes • At the same pressure and temperature, two gases of the same volume, contain the same number of molecules. • Or increasing the

20. Ideal Gas Law • PV=nRT To find R see pg 342 • Real vs Ideal gasses • Ideal gas assumes that molecules are hard small spheres that occupy no volume and have totally elastic collisions. • This isn’t true, but it’s a close approximation because atoms are very small, and tend to have nearly elastic collisions. • Ideal gas law works best at high temperature, low pressure and with non-polar gasses.

21. Molar Volume of a Gas • Recall avagadro: gasses at same volume pressure and temp have the same number of molecules… • STP: standard temperature and pressure: 1 atm and OoC • At STP one mole of gass occupies 22.4 Liters.

22. Vol 22.4 mol Converting volumes and moles at STP

23. Behavior of gases • Pressure: Force * area. Force comes from collisions of translating particles against the walls of their containers. • What effects pressure? • PV=nRT • Trends: • Units: T, n, V, and P • Pressure in Pascals (Pa), millimeters of mercury (mmHG), Atmospheres (atm), pounds per square inch (PSI), barr, torr, etc. • R = 0.82056 (L*Atm)/(K*mol)

24. Sample problems • What volume will 400 moles of a gas occupy at 300 K and 2 atm? • How many moles will fit in 22.414 L of gas at 273 K and 1 atm?

25. Convert these temperatures • 10 C • 27 C • 400 K • 400 C • 320 K • 180 C • 0 C

26. With temp conversions • If I have 1 mole of gas at 25 C, 0.5 atm what volume balloon would I need to trap the gas? • If I want to inflate a balloon to 10 L, and I’m at 25 C and 1 atm, how many moles do I need?

27. Try these • How many moles would be in 100 m3 at 4100 K and at a pressure of 13Pa? • What volume can 3 moles of gas at 300K fill at 3 atm? • What temperature (K) would 10 moles of gas be, if it is in a 30 m3 containor at 1000 Pa • What pressure (mmHG) would 0.4 moles of gas exert if it was 400 C and trapped in a 4 liter canister.? • How many moles are in 20 liters of gas at 20 atm and 2000 C? • What would the temperature (in celcius) be of 1 mole of gas occupying 1 liter at 10 atm of pressure? • What pressure would 3000 moles of gas in 0.5 m3 container, at –125 C? • What volume would a mole of gas at 10kPa and 420C occupy?

28. Ideal Gas Law • PV=nRT To find R see pg 342 • Real vs Ideal gasses • Ideal gas assumes that molecules are hard small spheres that occupy no volume and have totally elastic collisions. • This isn’t true, but it’s a close approximation because atoms are very small, and tend to have nearly elastic collisions. • Ideal gas law works best at high temperature, low pressure and with non-polar gasses.

29. Dalton’s Law of Partial Pressures • Dalton’s partial pressures: When you have a mixture of gasses, the total pressure of the mix will be equal to the sum of the pressures those gases would have if they were alone in the container.

30. Avagadro’s law of combining volumes • At the same pressure and temperature, two gases of the same volume, contain the same number of molecules. • Or increasing the