Lesson C2: Heat and the States of Matter

Key Ideas   Unit Checklist

  Video Lesson

Why do ice, liquid water, and steam look different although they are all made of water? Watch this video to learn how the appearance of a substance is affected by the movement of tiny particles within the substance.

Lesson C2: Heat and the States of Matter

Figure C.1.2.1 – Dry ice is solid carbon dioxide.
Figure C.1.2.2– At normal air pressure on Earth, carbon dioxide changes directly from a solid to a gas.
Dry Ice

Dry ice is solid carbon dioxide. Dry ice freezes at –79°C. This is much colder than ice made from water, which freezes at 0°C. Never touch solid dry ice with your bare hands because it will give you severe frostbite.

 An interesting feature of dry ice is that, when it is exposed to temperatures warmer than –79°C, instead of turning into a liquid it changes directly into carbon dioxide gas. The process of a substance changing from a solid to a gas is called sublimation.  

Dry ice is used to freeze food quickly, such as vegetables and fruit. This is called flash freezing. Dry ice is used in fog machines to produce special effects for theatre and film. Fog machines work by putting dry ice into warm water. Dry ice heats quickly in the warm water, and it changes into carbon dioxide gas. The fog comes from the machine as thick white clouds of carbon dioxide gas.
Reading and Materials for This Lesson:

Science in Action 7
Reading: Pages  190–197

Materials:
3 glass jars or cups, hot tap water, warm tap water, cold tap water, food colouring, 3 ice cubes, 3 bowls, teaspoon measuring spoon, table salt, sugar, timer

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Dry Ice

Watch this video to see some interesting science demonstrations using dry ice.


Liquid Nitrogen

Approximately 78% of the air on Earth is a gas called nitrogen. Just like water, nitrogen exists in various states as solid, liquid, and gas. However, substances change between states at different temperatures. For example, water melts and freezes at 0°C. Water changes between its liquid and gas states at 100°C.

The temperatures at which nitrogen changes states are much lower than those for water. For example, nitrogen changes between its liquid and gas states at –196°C. This is much colder than anywhere on Earth, which means that liquid nitrogen does not form naturally on Earth. Liquid nitrogen is made by using energy to force the nitrogen particles in air very close together into liquid form. The process of forcing gas particles to move closer together into a smaller space is called compression.
Figure C.1.2.3– Liquid nitrogen is stored in thick, insulated containers.

Liquid nitrogen must be handled very carefully. Because it is so cold, if you touch it, it freezes and kills body cells instantly. This property makes liquid nitrogen very useful, too. Sometimes doctors apply liquid nitrogen carefully to the skin to kill warts and skin cancer cells.

Figure C.1.2.4– As soon as a container of liquid nitrogen is opened, the solid ice starts changing into a gas.
Figure C.1.2.5– Liquid nitrogen is used to treat warts and skin cancer.

 Watch More

Liquid Nitrogen Experiments

Watch this video to see some interesting experiments with liquid nitrogen.



Liquid Nitrogen Ice Cream

This video explains how creamy smooth ice cream can be made using liquid nitrogen.

  Try It!

Particle Speed

Try this simple experiment to observe how particle movement changes at various temperatures.

Materials:

  • 3 glass jars or cups
  • hot tap water
  • warm tap water
  • cold tap water
  • food colouring

Instructions:

    1. Fill one glass jar with hot tap water.

    2. Fill one glass jar with warm tap water.

    3. Fill one glass jar with cold tap water

    4. Put one drop of food colouring into the water in each glass jar. Do not move or stir the water in the glass jars.

    5. Observe the movement of the food colouring in all three jars.

Questions:

Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.

The food colouring moved the fastest in the jar of hot water. The particles of food colouring moved quickly because they were heated by the hot water. With more energy, the food colouring particles spread quickly throughout the entire jar.
The food colouring moved the slowest in the jar of cold water. The particles of food colouring moved slowly because they were cooled by the cold water. With less energy, the food colouring particles spread less quickly throughout the entire jar.
Particles move faster at higher temperatures. Particles move slower at lower temperatures.


Figure C.1.2.6– Table salt is made of tiny crystals.
Figure C.1.2.7– The particles inside table salt are arranged in a repeating geometric pattern.

Crystals

A crystal is a solid that contains particles arranged in repeating geometric patterns. Because of the repeating particle patterns, crystals usually form flat faces and sharp edges. Not all solids form crystals. For example, crystal glass is not actually a crystal. The particles in crystal glass do not form a repeating geometric pattern.

Some crystals are common. Table salt and sugar are made of crystals. Viewed under a magnifying glass, salt is formed into cube-shaped crystals and sugar occurs as long prism-shaped crystals.

Some crystals are very rare. Gemstones are rare crystals mined from rock and used for jewellery. Blue sapphires, green emeralds, red rubies, and purple amethysts are examples of rare solid crystal gemstones. Diamonds are crystals, too, but diamonds are not as rare as many people think – or as rare as advertisers of jewellery want us to think!
Figure C.1.2.8– Amethyst is a purple crystal gemstone.

Figure C.1.2.9– Sapphire is a dark blue gemstone that is used in jewellery.
Figure C.1.2.10– Crystal glass is not made of crystals.

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Making Diamonds

Diamonds are very strong crystals, which means they are useful for purposes other than jewellery. Several industrial processes use diamonds. You may have seen someone using a diamond saw to cut ceramic tiles or stone, for example.

Now, scientists can make diamonds in a laboratory! Watch this video to learn more about diamonds.



Diamond Marketing

People think diamonds are very rare on Earth, which is why diamond jewellery is so expensive. In reality, diamonds are very common. Watch this video to find out how diamonds were marketed cleverly to have a higher value than they are actually worth.


Special Snowflakes

When water is a solid, it forms clear, colourless crystals. A large volume of liquid water will freeze into a large ice crystal, such as ice on a lake. Break a piece of ice and you have more crystals -- all smaller than the original, of course!

Snowflakes are small ice crystals that form in the air. A snowflake begins to form around a tiny particle of dust high in the atmosphere. A tiny drop of liquid water in a cloud freezes around the speck of dust. Additional water particles freeze to the snowflake crystal in a geometric pattern.
Figure C.1.2.11– Snowflakes form as patterns in hexagonal shapes.

Figure C.1.2.12– Snowflakes are colourless. In a pile, they reflect light to appear white.
Figure C.1.2.13– Ice is a large crystal.

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How Do Snowflakes Form?

Watch this video to see an animation of how snowflakes form.



Artificial Snow

Ski hills make artificial snow when natural snowfall is inadequate. Watch this video to learn how artificial snow is made.


Salt and Ice

During the winter, road maintenance workers often put salt on roads and sidewalks to melt slippery ice. When salt particles mix with water particles, the freezing point of the salt and water mixture drops below 0°C. The salt particles interfere with the ability of water particles to freeze into crystals.

Salting roads is most effective at temperatures between 0°C and -9°C. Salt is not as effective for clearing icy roads at colder temperatures.
Figure C.1.2.14– Salt is sometimes used to melt dangerous ice on roads. Photo by Michael Pereckas.

 Watch More

How Does Salt Melt Ice?

Watch this video to learn more about why salt melts ice.

  Try It!


Melting Ice

Try this simple experiment to see how various substances affect the melting rate of ice.

Materials:

  • 3 ice cubes
  • 3 bowls
  • teaspoon measuring spoon
  • table salt
  • sugar
  • timer

Instructions:

    1. Place 1 ice cube in each bowl.

    2. Add 2 teaspoons of sugar to one ice cube.

    3. Add 2 teaspoons of salt to a second ice cube.

    4. Leave the third ice cube alone.

    5. Start the timer. Observe how long it takes each ice cube to melt completely.

Questions:

Think about the following question very carefully. Then, type or write your answer. After you have your answer, click the question for feedback.

The ice cube with salt melted faster. The salt disrupted the geometric crystal pattern of the water particles in the ice cube. This lowered the freezing point of the ice cube and caused the ice cube to begin changing into water sooner.



  Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.

Unit C Lesson 2 Self-Check

Instructions


Complete the following 6 steps. Don't skip steps – if you do them in order, you will confirm your understanding of this lesson and create a study bank for the future.

  1. DOWNLOAD the self-check quiz by clicking here.

  2. ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.

  3. COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.

  4. REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.

  5. SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.

  6. CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!


Self-Check Time!
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Self-Check Quiz Answers

Click each of the suggested answers below, and carefully compare your answers to the suggested answers.

If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.

As a hot dog is heated on a fire, the water particles inside the hot dog begin to move faster and further apart. Some of the water in the hot dog changes from liquid to steam. If enough water particles gain enough energy to evaporate into steam, they push on the hot dog’s walls strongly enough to cause the hot dog to burst or split.
If the liquid particles inside an aerosol can are heated, they begin to move faster and further apart. The heated moving particles push more strongly on the inside of the metal aerosol can. If the particles in the can gain enough heat energy, they can exert sufficient pressure against the metal can to cause the can to explode. Flying metal from an explosion can hurt people and cause damage.
During the winter, air inside the soccer ball cools to a lower temperature. This means that the air particles inside the ball move slower and closer together, and the ball deflates.
When warm moist air cools suddenly, the gas water particles in the air begin to move slower and closer together. The steam in the air changes into very small drops of liquid in the air, which is called condensation. Small drops of liquid water in the air appear as a cloudy white fog.
When winter air cools overnight, gas water particles in the air begin to move slower and closer together. They change from a gas into tiny drops of liquid water, which process is called condensation. The drops of liquid water collect on cold car windows (and on everything else, too). If the car windows have a temperature of 0oC or lower, the liquid water drops freeze into small ice crystals. The small ice crystals are frost.