Chemical vs. Physical Changes

Before Video

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

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

• 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.

• 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

• 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).

• 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.

• 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.

• 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.

• 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.

• 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.

• 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 noise (the effect) as the hydrogen burns.

• A mixture contains two or more substances that are not chemically combined. Mixtures can be physically separated into their individual components. Examples include: Paper clips and staples mixed together, rocks and gravel, marbles and dice or salt and pepper.

• 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.