Today is Thursday, May 5 th, 2016

Transcription

1 In This Lesson: Unit 5 States of Matter (Lesson 1 of 3) Today is Thursday, May 5 th, 2016 Stuff You Need: Calculator Paper Towel Worksheets (see below) Pre-Class: What are the three (or four or five) states of matter? What do you call the transitions between the phases? Please take a scavenger hunt and vocabulary list. You will also need a small paper towel.

2 Today s Agenda Chapter 13 No, really. We re doing it all today. It s just vocabulary and concepts. Why cooking takes longer at higher altitudes. Where is this in my book? Uh, Chapter 13? P. 385 and following

3 By the end of this lesson You should be able to identify various properties and concepts relating to the three most common phases of matter. You should be able to convert between pressure and temperature units.

4 Phases of Matter There are four main phases of matter: Solids Ice Liquids Water Gases Water Vapor Plasma [Term 12] Plasma is similar to a gas and consists of ions at extremely high temperature. The surface of the sun is plasma.

5 Phases of Matter There are also Bose-Einstein Condensations. They re even weirder. Instead of being hot, they re extremely cool. All the atoms condense into a single, well, blob. Weird. There are actually many more phases of matter than just solid liquid gas plasma. Like degenerate matter, supersolids/superfluids, quark-gluon plasma, and Jahn-Teller metals. The difference? Only solids, liquids, gases, and plasma occur naturally.

6 Phase Transitions Going from a solid to a liquid is: Melting (also called fusion) Going from a liquid to a solid is: Freezing (also called solidification) Going from a liquid to a gas is: Boiling (or evaporation/vaporization) Going from a gas to a liquid is: Condensing Going from a solid to a gas is: Sublimation [Term 14] Going from a gas to a solid is: Deposition

7 Phase Changes Sublimation Melting (fusion) Freezing (solidification) Boiling (evaporation or vaporization) Condensation Deposition

8 Sublimation Demo To the fume hood! Let s watch as iodine crystals (solid) sublime into iodine gas. Note: Iodine gas (and iodine itself) is TOXIC. Another example of sublimation is dry ice. Video: Coin Into Dry Ice Still another example, in case you don t think you ve seen much sublimation in your life, is when snow and ice disappear from the ground despite the temperature being below freezing.

9 Phases of Matter We learned a long time ago that all matter has mass and anything with mass is probably matter. What about a location in which there is no matter? What s that called? It s a vacuum [Term 16]. No matter. Not even gas. Nothin. Like outer space!

10 Kinetic Theory Kinetic energy [Term 6] is the energy of motion. If you re running, you ve got a lot of motion. Kinetic theory [Term 7] states that all particles are in motion at all times, unless they re at 0 K (-273 C or F) absolute zero. Absolute zero has never been achieved, even in a lab. Still, we re pretty sure that if something were to reach 0 K, everything would stop. Closest achieved? K, or 100 picokelvins (pk). Okay technically there s a way to get below 0, but yeah.

11 Absolute Zero

12 Kinetic Energy and Temperature Temperature is a measure of the average kinetic energy of a substance s particles. The Kelvin temperature scale is used because it is proportional to the average kinetic energy of particles of a substance. Helium atoms at 200 K have twice the energy of Helium atoms at 100 K. How to calculate Kelvin? C = K C = K 273 Fun Fact: Technically, C = K

13 Gas Pressure Gas Pressure [Term 5] results from atoms or molecules in a container colliding with each other and the sides of the container. Atmospheric pressure [Term 1] is pressure from air molecules colliding with objects. At sea level, we re all under 14.7 lbs of air pressure!

14 Aside: Gas Pressure So how often do gas molecules collide? Down here at roughly sea level, a gas molecule moves an average of 3 millionths of an inch before it collides with another one. At the edges of the atmosphere, there may only be one or two molecules every few miles.

15 Measuring Atmospheric Pressure A barometer [Term 2] is used to measure atmospheric pressure. Air pushes down on mercury which rises up a glass tube proportionate to the pressure of the air.

16 Barometer

17 Atmospheric Pressure Is air pressure higher or lower at high altitudes? Consider this: Edge of Earth s Atmosphere Force of Air Lower Pressure Force of Air

18 Standard Atmosphere A Standard Atmosphere [Term 13] (or standard atmospheric pressure) is like room temperature except for pressure. Standard pressure is: 1 atmosphere (atm) 760 mm Hg 760 torr (named after discoverer of barometrics) kpa (kilopascals) pascal (Term 10) is the SI unit of pressure MEMORIZE THESE!

19 Aside: Blaise Pascal s Calculator Circa 1650:

20 Standard Temperature Standard temperature for gases is 0 C or 273 K. Therefore, Standard Temperature and Pressure (STP) is the combination of the two.

21 Pressure Unit Conversions Express kpa in torr. starting measurement target unit given unit kpa 760 torr kpa = 100 kpa = torr torr

22 Pressure Unit Conversions 2 atm =? torr =? mm Hg =? kpa 1520 torr, 1520 mm Hg, kpa 1.7 atm =? torr =? mm Hg =? kpa 1292 torr, 1292 mm Hg, kpa? atm =? torr = 800 mm Hg =? kpa 1.05 atm, 800 torr, kpa? atm =? torr =? mm Hg = 81 kpa 0.80 atm, 608 torr, 608 mm Hg

23 Vaporization or Evaporation? There s a difference. Thoughts? What if I told you it has to do with the temperature at which the process is occurring? Vaporization [Term 18] is when a liquid goes to a gas. Particles at the surface gain enough kinetic energy to break free from the liquid and become a gas. Evaporation [Term 4] is when a liquid goes to a gas when the liquid is not boiling.

24 Boiling Point Vapor pressure [Term 17] is the force of evaporated liquids in a sealed container. Liquid evaporates to gas, gas pushes on the container and liquid. Boiling point [Term 3] is the temperature at which the vapor pressure equals the atmospheric pressure. Causing bubbles to form as the liquid boils.

25 About Vapor Pressure How many of you have a propane tank and barbecue in the backyard? Okay, and how many of you know what phase of matter you ll find the propane in, inside the tank? Liquid? Gas? Turns out it s both! Propane is quite volatile, meaning it evaporates easily. Credit to Dr. Miller/Air Liquide 2016

26 About Vapor Pressure That means that there s a layer of propane gas above the rest of the propane liquid. That s variable by temperature, too, so in the winter there s less gas; in the summer there s more. The gas above the liquid is the vapor pressure. Let s look at how that changes. Credit to Dr. Miller/Air Liquide 2016

27 About Vapor Pressure At temperatures above the boiling point, water Imagine At 0 At achieves a Because C, At 100 balloon there 22 C, C, there s is that s an filled virtually even vapor the with about higher defined no pressure water as vapor much at boiling various grows pressure gas (not point! as and quite temperatures, there than there The 0, is but the liquid. is vapor close). hooked up to a The pressure vapor more gauge pressure has atmospheric headspace equaled to read is approximately the above pressure. atmospheric the liquid. 1 of atm. the pressure. gas Why? above the surface. ~ ~1 1.4 atm atm atm atm 0 C 22 C 100 C 110 C Credit to Dr. Miller/Air Liquide 2016

28 Thinking About Vapor Pressure Can evaporation occur below the freezing point? As in, can snow/ice slowly disappear anyway? Yep, even solids have vapor pressure, ice included. Even iron has a vapor pressure, though very low. If we take a pan of water to the summit of Mount Everest, how will that change the boiling point? Since atmospheric pressure is so low, the boiling point is also much lower. The water would boil at about 72 F!

29 Boiling Point Normal boiling point [Term 9] is the boiling point of a liquid at standard pressure (101.3 kpa). In Doylestown, at standard pressure, water boils at 100 C. In Denver, at lower pressure (higher altitude so less air above), water boils at 95 C. So cakes take longer to bake because temperature must be kept lower. This is also how pressure cookers work, in a way.

30 Low Boiling Points Nitrogen is most commonly found as a gas, but that s only because it s got a VERY low boiling point. Nitrogen boils at -196 C ( F). Below that temperature, it s a liquid liquid nitrogen. Video!

31 Melting Point Melting point [Term 8] is the temperature at which a solid becomes a liquid. Once again, a friendly reminder that melting is also called fusion.

32 Phase Diagram Phase diagrams [Term 11] show the relationship between pressure, temperature, and the three phases of matter for a chemical. The triple point [Term 15] is the point at which all three phases can exist at the same time. Video: Water Boils and Freezes at the Same Time

33 Phase Diagram of Water

34 Heating/Cooling Curve Similarly, a heating/cooling curve shows the temperature and energy of a substance over time as it goes through phase changes.

35 Closure In addition to the notes you took today, I will be posting this PowerPoint and a key to the vocabulary sheet. It s not all necessary to know, but it may help you understand terms you didn t in class. My Website > Chemistry > Worksheets and Keys.