When the thermometer is cooled, the molecules move more slowly, get closer together, and move down in the tube. When the thermometer is heated, the molecules move faster, get slightly further apart, ...

Some chemical reactions change temperature, change color, produce a gas, or make a solid from two liquids. Try this reaction and see what it does! Pour 1 tablespoon of hydrogen peroxide into a cup.

The temperature on the thermometer has fallen, meaning it is an endothermic reaction. When ammonium chloride powder is mixed with barium hydroxide powder and stirred, a chemical reaction takes place.