gizmo warm-up a chemical change, (or chemical reaction) occurs when one or more substances, called reactants, are transformed into different substances, or products. in the chemical changes gizmo, you will look for evidence of chemical changes by looking at changes you can see, touch, or smell. to begin, check that reactant 1 is sodium and reactant 2 is water. sodium is a metal so soft you can cut it with a knife. click play (). what do you observe? the mass increased science. we took sodium and added it to the water. do you think a chemical reaction has taken place? explain.