When liquids such as water or vinegar evaporate, they release a gas called _________________.
The green substance that sometimes forms on the surface of a penny is called _______________.
People can rub silver polish on their silverware so that it will not turn black or ________________.
When iron is exposed to air and moisture, a reddish substance called ___________begins to form,
When one kind of matter is changed into a different kind of matter, that is a __________________.
Chemical changes always involve_______________.
Some chemical changes can be harmful.
Some chemical changes can be helpful.
Describe what happens when sodium and chlorine combine?
How is a chemical change different from a physical change?