Here's why:

* Mixtures are combinations of substances that are physically combined, not chemically bonded. This means they can be separated by physical means like filtration, evaporation, distillation, or magnetism.

* Chemical change involves the formation of new substances with different chemical properties. This happens when atoms rearrange and form new bonds.

Think of it this way:

* Mixture: Imagine a bowl of sand and sugar. You can easily separate them by using a sieve or by dissolving the sugar in water.

* Chemical Change: Imagine baking a cake. You mix flour, sugar, eggs, and other ingredients. When you bake the cake, a chemical change occurs, and the ingredients are transformed into a new substance (cake) with different properties. You can't easily separate the original ingredients from the cake.

To separate a mixture, you need to use physical methods that exploit the different physical properties of the components.

Let me know if you have any other questions!