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Discover how atoms can rearrange themselves to create brand new substances.
Have you ever wondered why a shiny silver bicycle turns crusty and orange if left in the rain, or how a gooey yellow egg becomes a solid white breakfast?
Imagine you have a box of LEGO bricks built into a car. If you take it apart and build a plane, you still have the same bricks, but the shape is different. In a chemical change, the "bricks" (called atoms) actually trade places with each other to make something totally new! A chemical reaction is the process where this happens. Unlike a physical change, like ice melting into water, you cannot easily turn a chemical change back. Once you bake a cake, you can't turn it back into flour and eggs because the atoms have rearranged into a new substance.
Quick Check
What is the main thing that is created during a chemical change?
Answer
A brand new substance.
How do we know a reaction is happening if we can't see the tiny atoms? Scientists look for clues. One clue is gas production, which looks like bubbles or smoke. Another clue is a temperature change—some reactions get hot, while others get cold. A third clue is a color change. If you see a liquid turn from clear to bright blue without adding dye, a chemical reaction is likely happening! These signs tell us that the atoms are busy moving around to form something different.
Mixing baking soda and vinegar is a classic chemical reaction. 1. Start with a solid (baking soda) and a liquid (vinegar). 2. When mixed, they react to form a gas called Carbon Dioxide (). 3. You see the clue: hundreds of tiny bubbles foaming up! 4. Because a new gas was made, this is a chemical change.
Quick Check
If you see bubbles forming when you mix two liquids, what might be happening?
Answer
A chemical reaction is producing a gas.
It is important to tell the difference between a physical change and a chemical change. In a physical change, the substance stays the same, even if it looks different. For example, if you shred paper, it is still paper. If you freeze water into ice ( solid), it is still water ( liquid). But if you burn the paper, it turns into ash and smoke. Burning is a chemical change because ash is a completely different substance than paper!
Leaving an iron tool outside in the rain causes a reaction. 1. The Iron () atoms in the tool touch Oxygen () atoms from the air and water. 2. They bond together to create a new substance called Iron Oxide (), or rust. 3. You see the clue: a color change from silver to orange-brown. 4. You can't simply 'un-rust' the metal back to its original form easily.
Think about a campfire burning a log. 1. The heat causes the wood to react with Oxygen (). 2. Energy is released as light and heat (you feel the warmth!). 3. The wood turns into black charcoal, grey ash, and invisible gases like Carbon Dioxide (). 4. This is a complex chemical reaction because multiple new substances are created at once.
Which of these is a sign that a chemical reaction is happening?
What happens to atoms during a chemical reaction?
Melting an ice cube is a chemical change.
Review Tomorrow
In 24 hours, try to name the three 'clues' that tell you a chemical reaction is happening.
Practice Activity
Go on a 'Change Hunt' in your kitchen. Can you find one physical change (like cutting a sandwich) and one chemical change (like toasting bread)?