Pressure, Temperature,& Phase Change
How do you read a phase diagram?
Why?
Not only temperature but pressure can change the phase of matter between a solid, liquid and gas.
The relationship between the two variables can be shown in a phase diagram. When all three lines
come together at the triple point this indicates the substance is in all three phases: solid, liquid, and gas
at the same time. In this demonstration you will learn how to change the phase of a substance by
decreasing or increasing the pressure.
Phase Diagram of Water
1. What substance is this phase diagram for? __________________
2. At 1 atmosphere (atm) pressure, what temperature does water melt?_____________________
3. At 1 atmosphere (atm) pressure, at what temperature does water boil (evaporate to gas)?______
4. At 0.1 atmospheres (atm) pressure (10-1), at what temperature does water boil?____________
5. What happens to boiling point temperature as the pressure goes down? __________________
6. At 10 atmospheres (atm) pressure, what temperature does water boil?________________
7. What happens to the boiling point temperature as the pressure goes up? ______________
8. What happens at the triple point? _________________________________________________
9. What is the pressure of water at its’ triple point? _____________
10. What is the temperature of water at its’ triple point? __________________
11. Room temperature is about 25 Celsius. According to the phase diagram, what does the pressure
of water have to be in order to get it to boil (evaporate to gas) at this temperature? _________
12. A phase change (from solid to liquid to gas) is a physical/chemical change. (circle the best
choice)
13. What will happen to the following when placed under the vacuum?
a. Water b. Marshmallow c. balloon
d. Shaving cream (do last)
e. liquid N2
Read This!
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Dry ice is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include
lower temperature than that of water ice and not leaving any residue (other than incidental frost from
moisture in the atmosphere). It is useful for preserving frozen foods, ice cream, etc., where mechanical
cooling is unavailable.
Dry ice sublimates at −78.5 °C (−109.3 °F) at atmospheric pressure. This extreme cold makes the solid
dangerous to handle without protection due to burns caused by freezing (frostbite). While generally not
very toxic, the outgassing from it can cause hypercapnia due to buildup in confined locations.
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Phase Diagram of Carbon Dioxide
1. What substance is this phase diagram for? _______________
2. CO2 behaves differently at 1 atmosphere (atm) pressure than water. What is different about
how solid CO2 behaves at 1 atmospheric pressure?_________________________________
3. What is the pressure of CO2 at its triple point?_____________________
4. What is the temperature of CO2 at its triple point?_______________________
5. What do we have to do to the pressure of solid CO2 (dry ice) to melt it?
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Liquid nitrogen is nitrogen in a liquid state at an extremely low temperature. It is produced industrially by fractional distillation of liquid air.
Liquid nitrogen is a colorless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.43.[1] Liquid nitrogen is
often referred to by the abbreviation, LN2 or "LIN" or "LN" and has the UN number 1977.
At atmospheric pressure, liquid nitrogen boils at −196 °C (77 K; −321 °F) and is a cryogenic fluid which can cause rapid freezing on contact with
living tissue. When appropriately insulated from ambient heat, liquid nitrogen can be stored and transported, for example in vacuum flasks.
Here, the very low temperature is held constant at 77 K by slow boiling of the liquid, resulting in the evolution of nitrogen gas. Depending on
the size and design, the holding time of vacuum flasks ranges from a few hours to a few weeks.
Liquid nitrogen can easily be converted to a solid by placing it in a vacuum chamber pumped by a rotary vacuum pump.[2] Liquid nitrogen
freezes at 63 K (−210 °C; −346 °F). Despite its reputation, liquid nitrogen's efficiency as a coolant is limited by the fact that it boils immediately
on contact with a warmer object, enveloping the object in insulating nitrogen gas. This effect, known as the Leidenfrost effect, applies to any
liquid in contact with an object significantly hotter than its boiling point. More rapid cooling may be obtained by plunging an object into a slush
of liquid and solid nitrogen rather than liquid nitrogen alone.
Nitrogen was first liquefied at the Jagiellonian University on 15 April 1883 by Polish physicists, Zygmunt Wróblewski and Karol Olszewski.[3]
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Phase Diagram of Nitrogen
What is this a phase diagram for? ________________________________
At one atmosphere pressure, what is the temperature of liquid nitrogen?____________________
3. How can we get to the triple point of nitrogen?_________________________________
4. What will happen to the following items when dipped in liquid N2?
a. Banana
b. Flower
c. Tennis ball
1.
2.