Next Generation Science Videos for Grades K-5Grades K-5Key Stage 1 & 2Years F-6.

Sample Lesson: Chemical vs. Physical Changes

• Discussion Questions

  • Before Video

    How are chemical changes different from physical changes?ANSWER

    • Chemical changes happen when substances change to form new ones, while physical changes do not form any new substances.

    Is toasting a piece of bread an example of a physical or chemical change?ANSWER

    • Heating bread in a toaster is a chemical change. The surface of the bread burns, forming a new substance.

    When the banana, berries, water and hot dog are blended, does a physical or chemical change occur? Why?ANSWER

    • Blending the banana, berries, water and hot dog chops them up into tiny pieces, but doesn’t create a new substance. Therefore, it is an example of a physical change.

    Is water evaporating an example of a physical or chemical change?ANSWER

    • Evaporation means to turn a liquid into a gas. Water in gas form is not a new substance (it is still water) so that makes it a physical change.

  • After Video

    What happens when Zoe stirs the very hot water with the spoon made from Gallium metal? What kind of change happens?ANSWER

    • When Zoe stirs the hot water with the Gallium spoon, the metal melts. This is an example of a physical change because the Gallium changed forms, but it didn’t change into a new substance (it is still Gallium).

    What kind of change happens when Dr. Jeff puts the gummy candy into a tube containing oxidizer? Why?ANSWER

    • When Dr. Jeff drops the gummy candy into the tube containing oxidizer, the gummy candy bursts into flames producing smoke and carbon (new substances). Therefore, this is a chemical change.

    What method did the team use to test what type of gas was produced in the reaction between the Mentos and soda?ANSWER

    • Dr. Jeff, Izzy and Zoe used a balloon to collect some of the gas produced when soda and Mentos were combined. They then tested this gas to determine its properties. They concluded that it was carbon dioxide by observing that it extinguished candles.

    When Zoe pours the carbon dioxide gas onto the candles, why do they go out one by one?ANSWER

    • Carbon dioxide gas is heavier than air. This is why it stays inside the pitcher. When Zoe pours it at the top of the steps, it flows down the steps because it is heavier than the air that was there. When the carbon dioxide displaces the air, the candle doesn't have enough oxygen, so it goes out. This process happens to each candle as the carbon dioxide sinks lower and lower.

    What evidence did the team find that the reaction between the Mentos and soda was a physical change?ANSWER

    • It was unclear at first whether the reaction that caused the soda to fizz uncontrollably was a chemical or physical change. The team investigated and determined that the gas produced was carbon dioxide, which is the same gas already used to make the soda fizzy. That means it is not a new substance, making this a physical change.

    What is a flame test and what can we learn from it?ANSWER

    • A flame test is a way to tell different types of gases apart. Scientists know how different types of gas will react when exposed to a flame. For example, oxygen would make the match glow brighter, carbon dioxide would make it go out and hydrogen can burn so it makes a POP sound when next to a flame. These are the most common gases tested in a flame test but there are others as well.

    Explain how the reaction of a flame to carbon dioxide is different than the reaction of a flame to hydrogen in terms of cause and effect. ANSWER

    • Carbon dioxide displaces the oxygen the flame needs to burn, which causes the flame to go out (the effect). When a flame is placed near hydrogen, it causes a popping sound (the effect) as the hydrogen burns.

    Why is whipping egg whites a physical change? ANSWER

    • Whipping egg whites simply adds air into the egg whites, making them foamy. They are still egg whites (not a new substance) so this is a physical change.

• Vocabulary
  • Catalyst DEFINE

    A substance that speeds up a chemical reaction.

  • Chemical Change DEFINE

    A type of change in which a new substance is formed. For example: burning something.

  • Physical Change DEFINE

    A type of change in which a new substance is NOT formed. For example: water boiling.

  • Oxidizer DEFINE

    A chemical that provides a lot of oxygen to help things burn.

  • Carbon Dioxide DEFINE

    A gas without any color or smell that is commonly found in soda. It is also called CO2 and comes out the back of a car or bus that is running.

  • Hydrogen DEFINE

    A gas less dense than air that has no color or smell. It is extremely flammable meaning it can burn.

  • States of Matter DEFINE

    The main forms matter can exist in: Solid, Liquid and Gas (also plasma but that is less common on earth).
    

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