Question

How can we tell if a chemical change has taken place?

Answer 1

Well, the tell-tale indicator of a chemical change is colour change.....

Explanation:

Chemical change is characterized by the formation of new substances, and the making and breaking of strong chemical bonds. In practice, this entails macroscopic colour change, or formation of an insoluble precipitate, or the visible evolution of a gas.

Of course chemistry is an experimental, hands-on science, and synthetic chemists closely monitor their reaction mixtures for signs of reaction, and for indicators of completion of reaction. And of course sometimes (in fact most of the time) A CHEMICAL REACTION DOES NOT OCCUR.

It is a sobering fact that when you look at `"Ph.D."` theses in the academic environment, most of the chemistry described could be completed in 4-6 weeks. Of course, the chemistry described in the experimental is the distillation of 3-5 years of failed experiments, and dead-ends, and disasters.