Chemical reactions | Middle school chemistry | Khan Academy

What is the main difference between a physical change and a chemical change?

• Physical changes create new substances, while chemical changes do not.

• Chemical changes create new substances, while physical changes do not.

• Physical changes involve breaking bonds, while chemical changes involve forming bonds.

• Chemical changes are always reversible, while physical changes are not.

What happens to atoms during a chemical reaction?

• Atoms are destroyed and new atoms are created.

• Atoms change into different types of atoms.

• Atoms are rearranged to form new substances.

• Atoms remain in their original arrangement.

In a chemical reaction, what are the substances present before the reaction occurs called?

• Products

• Elements

• Reactants

• Compounds

What happens to the total mass of substances during a chemical reaction?

• The total mass increases.

• The total mass decreases.

• The total mass remains the same.

• The total mass can either increase or decrease depending on the reaction.