# Good Morning 5/5/2015 Due today: The Chapter 10 Packet and the Liquid Nitrogen Worksheet. I’ll be coming around to check your packet with the clip board.

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Good Morning 5/5/2015 Due today: The Chapter 10 Packet and the Liquid Nitrogen Worksheet. I’ll be coming around to check your packet with the clip board while you go through the answers to the and the Liquid Nitrogen Worksheet on a the laptops. This is so that you will have your packets to help you study for tomorrows test. The Liquid Nitrogen Worksheet will be turned in at the end of the period. (you won’t need these to study for tomorrows test)

First Help for the test You will need to study the Ch 10 Notes, if you have blanks the PPT for this is on Homework Live. In addition you should be up on the following topics (the packet may help) Kinetic Energy = Temperature (this works perfectly in Kelvin) Relate this to Absolute Zero (you’ll have to know what absolute zero is to do this) Know where on the planet the air pressure is the greatest and lowest.

Things you need to know continued Know what it means to have Equilibrium between evaporation and condensation. Know that Particles only change state (gas, liquid, solid) when they have enough Energy. Know the phase of ionic compounds at Room temperature and why. Figure out how to get liquid water at a temperature above 100 0 C The test will be only multiple choice. There will be a conversion question but you will have to choose the proper set up not do the calculation.

Tomorrow Bring your book so that you will be able to work on the assignment for the next chapter after you are done with your test. To open the ppt. You need to go to Science shares, then Durand, then Chem, then States of Matter. Finally click on the Liq Nitrogen Answers PPT.

Liquid Nitrogen Worksheet Study Guide Questions to the Cryogenic Articles

1. Define temperature: A measure of how “hot” or “cold” something is in degrees. A measure of the average kinetic energy of a substance.

2. In which direction does heat flow? From HOT to COLD.

3. What is the triple point of water? 273.16 K or 0.16  C. At this temperature water, ice, and water vapor all exist together. In other words, the solid, liquid and gas phases of water coexist in equilibrium.

4. What is absolute zero? The theoretical temperature at which the atoms and molecules of a substance have the least possible energy. 0 Kelvin or -273.15  C or - 459.67  F

5. Which temperature scale is the international standard for scientific temperature measured? Kelvin scale.

6. What is the lowest recorded temperature to date? 0.000 01 Kelvin This may be outdated by now, but let’s go with it anyway. : )

7. At what temperature does air become a liquid? Air becomes a liquid at about –190  C

8. What are the components of liquid air? 78% Nitrogen, 21% Oxygen, and 1% Argon

9. What temperature range does cryogenics study? At –100  C or lower. Also allow: –285.3  F or –176.1  C and lower.

10. Identify one primary use of liquid oxygen. High energy fuels for rocket engines that power spacecraft.

11. What happens to iron and plastics when exposed to liquid air? They become brittle. Proof of this was seen in class with the plastic tubing.

12. What happens to copper and brass when exposed to liquid air? They become tougher.

13. How does exposure to liquid air affect a metal’s electrical conductivity? They become better conductors of electricity.

14. How does exposure to liquid air affect a metal’s magnetic strength? It increases the strength of the magnet.

15. How can you measure the temperature of liquid air? (a mercury thermometer would freeze solid). The most accurate thermometer that measures the temperature of liquid air is the platinum resistance thermometer. A P.R.T. measures temperature by determining its effect on the electrical resistance of platinum. Platinum becomes a better or poorer conductor of electricity as its temperature changes.

16. Liquid air is a mixture of 78% Nitrogen and 21% Oxygen. How can you separate the liquid nitrogen from the liquid oxygen in liquid air? Since Nitrogen and Oxygen have different boiling points, you can use distillation to separate them.

17. Describe the Joule -Thomson expansion method for liquefying air. Compressed air flows through a series of throttling valves into increasingly larger containers. The pressure and temperature of the air decreases in each chamber as the air expands. In the final chamber, some of the air has become cold enough to condense into a liquid.

18. Identify the name of the special container that protects the liquid air from heat and evaporation. Dewar flask.

19. How is liquid nitrogen used in cryosurgery? Liquid nitrogen is used to kill unhealthy tissue by freezing. Like warts : )

20. The lowest possible temperature 0 Kelvin is equivalent to - 273.16  C and - 459.69  F.

21. Where is the Rankine temperature scale used? The Rankine scale is used for certain kinds of engineering work like the aerospace industry.

22. Identify the temperatures for carbon dioxide (dry ice) Solidifying and the freezing point of Mercury. Carbon solidifies at - 79  C The freezing point of Mercury - 39  C.

23. How does cooling by demagnetization work? A strong magnetic field provides outside energy to line up the molecules of a paramagnetic crystal. This also raises the temperature. When the crystal cools back to the starting temperature, the field is removed and the molecules swing back to a disorderly arrangement. The energy they use to move comes from the heat energy of the crystal, so the temperature drops.

24. What are some of the properties of super-fluid helium? Superfluid helium runs quickly through tiny holes that would slow normal liquids. It also defies the laws of gravity by creeping up the sides of a container. It also conducts heat a thousand times more efficiently than copper.

What is a superconductor? Metals and metal alloys in which electrical resistance completely disappears when cooled to temperatures below about 20 Kelvin.

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