21) PHASE CHANGE: a change from one state (solid or liquid or gas) to another without a change in chemical composition.

Transcription

1 21) PHASE CHANGE: a change from one state (solid or liquid or gas) to another without a change in chemical composition.

2 22) Show that you understand how phase changes occur by writing an explanation for the following event: You forgot to turn off the teakettle and now the water is all gone. Heat increased the KE of the water particles causing the space between water particles to increase which led to water particles changing phase to gas particles.

3 23) Pants were hung on a clothesline overnight and the temperature dropped below freezing The pants lost heat to the environment and then the water particles changed from liquid to solid.

4 The entertainment industry has a popular use for dry ice. The fog used in special effects is made with dry ice. When ice comes into contact with water, it condenses and forms a thick white fog. A lesser know use for dry ice has to do with controlling mosquitoes and wood beetles. These insects are attracted to CO2 and naturally flow towards dry ice. Place come dry ice around a mosquito trap to reduce their population.

5 When dry ice heats up it sublimates into carbon dioxide gas, which is a normal component of air. Dry ice is C. If you were to touch dry ice the heat from your hand would be absorbed by the dry ice. If you hold dry ice you will get severe frost bite - damaging your skin much the same way as a burn. Dry ice is cold enough to kill cells and cause serious injury so treat it with respect and handle it with care. As always, DO NOT PUT LAB CHEMICALS IN YOUR MOUTH and KEEP YOUR GOGGLES ON!

6 Consider: color, phase change, density, uses in real life DRY ICE ICE

7 Consider: color, phase change, density, uses in real life DRY ICE ICE Carbon dioxide Both are used for cooling Water = H 2 O Sublimates at C Melts at 0 C Sublimates at C Created naturally

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9 PHASE CHANGE DIAGRAM GAS LIQUID SOLID

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11 Boiling water. Evaporation happens only at the surface of a liquid and occurs at any temperature (so long as the substance is a liquid at that temperature). However, as most people are aware, liquids evaporates faster at a higher temperature. Boiling, on the other hand, happens throughout the bulk of a liquid, usually starting from some site on the inside of the container and rising in a bubble to the surface. It only happens when the temperature is above the boiling point of that substance. What are the microscopic differences? Boiling occurs when the average motion of particles is fast enough to overcome the forces holding them close together. This happens evenly throughout a boiling liquid because the temperature is uniform throughout.

12 PHASE CHANGE DIAGRAM GAS LIQUID Melting Freezing SOLID

13 Types of phase changes Solid è Gas Gas è Solid Liquid è Gas Gas è Liquid Solid è Liquid Liquid è Solid Sublimation Deposition Vaporization (Evaporation) Condensation Melting Freezing

14 Types of phase changes Solid è Gas Gas è Solid Liquid è Gas Gas è Liquid Solid è Liquid Liquid è Solid Sublimation Deposition Vaporization (Evaporation) Condensation Melting Freezing

15 Real life examples of phase changes FREEZING: MELTING: EVAPORATION (vaporization): CONDENSATION: SUBLIMATION: DEPOSITION:

16 Real life examples of phase changes FREEZING: When water loses heat to a colder environment (0 centigrade or lower) MELTING: Eating an ice cream cone when its hot out EVAPORATION (vaporization): After it rains there are puddles but then when the sun comes out the puddles are gone CONDENSATION: When you have an ice cold drink in the summer little beads of water form on the outside of the glass. Also clouds SUBLIMATION: If you heat a metal fast enough (or dry ice) it will skip the liquid phase and go straight to vapor DEPOSITION: Water vapor turns into frost when its below 0 centigrade.

17 Quiz Answers 1) Demonstrate your understanding of the concepts and objectives of the Building a Thermometer lab by accurately using each of the words below in a paragraph explaining this lab. Thermometer, heat, temperature, kinetic energy, expansion, contraction.

18 2) T c = 10 C, T H = 70 C, Distance between cold and hot lines = 6 cm. What is the calibration for this thermometer? ( C/cm) 3) Students who recorded the data in #2 also found that the distance from the cold line to the line representing room temperature was 1.5cm. Room temperature = C

19 4-6) States of Matter: The difference between these states has to do with how tightly particles are packed together and how they move. For each of the pictured states of matter, name it as a gas, liquid, or solid and describe how its particles move. Also say whether or not the substance would have a definite shape. Solid Particles vibrate but do not change positions Liquid Particles have enough energy to change position by sliding over each other (9lowing) Gas Particles have enough energy to overcome attractive forces

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21 16) A student measures the mass of an object as 50 grams, and the objects volume as 25 cubic centimeters. What is the density of the object? (Include the correct units!!)

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