Stuff is changing around you all the time. Some changes are sneaky — like ice melting into water, which is still just water wearing a different outfit. But sometimes something deeper happens: the ingredients themselves get rebuilt into brand-new stuff. That's a chemical reaction. So how do you catch one in the act?

Here's the secret. A chemical reaction leaves clues — like footprints at a crime scene. No single clue is proof on its own, but when you spot a few of them together, you can be pretty sure new matter was just born. Detectives have five favorite clues to look for.

Clue number one: a sudden color change. When you slice an apple and it slowly turns brown, that's not dirt or a trick of the light. The apple's insides are reacting with oxygen in the air, building a new brownish substance that simply wasn't there before.

Clue number two: bubbles, where no one is blowing them. When you drop an antacid tablet into water and it hisses into fizz, the bubbles are a brand-new gas being made right in front of you. A real reaction can build a gas out of solids and liquids, like pulling a rabbit from a hat.

Clue number three: heat or cold you didn't add. Some reactions get warm or even glow, like a campfire turning wood into ash and warmth. Others go surprisingly cold, pulling heat out of their surroundings. If a mixture changes temperature all by itself, something chemical may be cooking.

Clue number four: a new smell. When toast goes from soft bread to that warm, nutty, slightly toasty scent, the heat has rebuilt the bread's molecules into new ones — and your nose catches the difference. A fresh smell often means fresh substances.

Clue number five: a solid that appears out of clear liquids. Mix two see-through liquids and sometimes a cloudy snow drifts down inside the glass. Scientists call it a precipitate — a brand-new solid that the reaction quietly knitted together from things that were dissolved.

But beware the impostors! Boiling water makes bubbles too, yet it's still water — just hot. Melting chocolate looks dramatic but stays chocolate. The real test is whether you've made something genuinely new, something you can't simply un-do by cooling it back down.

So here's the big idea. A physical change rearranges the same stuff — same Lego bricks, new shape. A chemical reaction takes the bricks apart and snaps them into a different model entirely. The five clues are your way of peeking at the rebuilding while it's happening.

Now look again at that fizzing glass from the start. The bubbles, the warmth, the new smell — those aren't random sparkles. They're the world quietly announcing it just invented something new. Once you know the clues, you'll spot chemistry everywhere: in your kitchen, your garden, even in a slice of browning apple.