A chemical reaction forms new substances and is indicated by signs such as light, heat, color change, gas production or odor. A physical reaction only changes a substance's appearance and can be reversed to the original state. Chemical reactions occur through bonding or breaking bonds and involve energy, while physical changes alter a substance's form without changing its chemical makeup.

1. Chemical and Physical
Reactions quiz.

2. 1. What is a chemical
reaction?
• A chemical change makes a
substance that wasn't there
before. There may be clues that
a chemical reaction took place,
such as light, heat, color
change, gas production, odor, or
sound.

3. 2. What is a physical
reaction?
• A physical reaction is the
change in the appearance of an
object in which it can change
back to it's original state.

4. 3. How are chemical
reactions formed?
• A chemical reactions is the
process by which objects bond
together (or break bonds) and,
in doing so, either release or
consume energy.

5. 4. How are physical
reactions formed?
Physical changes occur when
objects take a change that does
not change their chemical
nature.