A chemical change is when a substance transforms into a completely new substance, and it can't be reversed. For example, when you burn a piece of paper, it turns into ash, and you can't turn that ash back into paper. So, is boiling an egg similar to burning paper? Well, not exactly, but it's still a pretty interesting transformation.
The thing is, when you boil an egg, the heat causes the chemical bonds in the egg to break and reform into new bonds. This process is called coagulation, and it's what makes the egg white and yolk change from a liquid to a solid. It's like when you're building with Legos, and you take apart a structure, and then rebuild it into something entirely new - the chemical bonds are like the Legos, and the heat is like the builder.
