Identifying Physical and Chemical Changes – Quiz Edition

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Every day, we see many changes happening all around us. Snow melts on a warm spring morning, your breath fogs up a window on a cold day, and cookie dough transforms as it bakes in the oven. These changes, big or small, show us that matter is always changing.
In science, we study these changes and put them into two main groups: physical changes and chemical changes.

Chemical changes happen when something turns into a new substance with different properties. These changes often give off or take in energy, like heat, light, or sound. We can usually tell if a chemical change happens by looking for clues like a change in color, bubbles forming, or a solid appearing in a liquid.

Imagine a marshmallow being roasted over a campfire. As the marshmallow heats up, it turns golden brown and becomes gooey. The sugar in the marshmallow is changing into new substances, creating that yummy toasted flavor. The heat and the color change tell us this is a chemical change.

Now think about a shiny new bicycle left outside in the rain. Over time, the metal parts start to rust, turning a reddish-brown color. This happens because the metal reacts with the oxygen and water in the air, making a new substance called rust. The color change and the new substance show us a chemical change.
When you mix baking soda and vinegar, you get a bubbly surprise! The two substances react to make a new substance called carbon dioxide, which forms all those fizzy bubbles. The bubbles and the new substance are signs of a chemical change.

On the other hand, physical changes happen when something changes its shape or state, but it's still the same substance. No new matter is made. Imagine a big block of clay. You can squish it, roll it, and mold it into different shapes, but it's still clay. The shape changes, but the substance stays the same. That's a physical change.

Now think about a glass of water. When you put it in the freezer, the water turns into solid ice. It changes from a liquid to a solid, but it's still water. The change in state is a physical change.

When you tear a piece of paper into smaller pieces, you're making a physical change. The size and shape of the paper change, but it's still paper. Each tiny piece is still made of the same stuff as the big piece you started with.

Lastly, imagine an elastic hair tie. When you stretch it, it changes shape, getting longer and thinner. But when you let go, it snaps back to its original shape. The stretching is a physical change because the hair tie is still the same substance, just a different shape.


Do you think you can identify changes to matter as either physical changes or chemical changes? Let's put your knowledge to the test!

Crumpling a Sheet of Paper
Physical Change
When a sheet of paper is crumpled into a ball, its shape changes, but its composition remains the same. The paper is still made of cellulose fibers, so this is a physical change.

Baking Pizza
Chemical Change
When pizza dough, sauce, and cheese are baked in the oven, the heat causes chemical reactions that change the texture, color, and flavor. The dough rises, the cheese melts and browns, and new substances form, making this a chemical change.

Rusting of a Bike Chain
Chemical Change
When a metal bike chain is exposed to air and moisture, it forms rust. This is a chemical change because a new substance, iron oxide (rust), is formed through a reaction between the metal and the environment.

Melting Ice Cream
Physical Change
On a hot day, ice cream melts and changes from a solid to a liquid state. This is a physical change because the composition of the ice cream remains the same; only its state changes.

Cutting Hair
Physical Change
When hair is cut, the length and style may change, but the chemical composition of the hair remains the same. This is a physical change.

Sharpening a Pencil
Physical Change
When you sharpen a pencil, the shape and size of the pencil change, but the wood and graphite remain the same substances. This is a physical change.

Burning a Candle
Chemical Change
When a candle burns, the wax melts (a physical change), but the flame also creates smoke and gases like carbon dioxide. This is a chemical change because new substances are formed that cannot be changed back into wax.

Ripening of a Banana
Chemical Change
As a banana ripens, its peel turns from green to yellow to brown. This color change is a result of chemical reactions inside the fruit, which also cause changes in texture and flavor. The formation of new substances makes this a chemical change.