Chemical Reactions Unit Review

Nevaeh is having a bonfire. What is happening to the atoms in the wood:

• The atoms in the wood are getting destroyed.

• The atoms in the wood are rerranging to form new substances.

• Some atoms are being destroyed, some are being created.

Answer explanation

Law of Conservation of Mass: Atoms cannot be created or destroyed.

True or False: Atoms can be destroyed in a fire.

• True

• False

Answer explanation

Law of Conservation of Mass: Atoms cannot be created or destroyed

What elements are in this molecule: C8H10N4O2

• Carbon, Helium, Sodium, Oxygen

• Carbon, Hydrogen, Sodium, Oxygen

• Carbon, Hydrogen, Nitrogen, Oxygen

• Calcium, Hydrogen, Nitrogen, Oxygen

What elements are in this molecule: CaCl2?

• Calcium and Chlorine

• Carbon and Chlorine

• Calcium and Steel

• Carbon and Steel

Chemical or Physical Change: Melting an Ice Cube

• Chemical Change

• Physical Change

Answer explanation

When melting, atoms are not rearranging. They are simply speeding up.

Chemical or Physical Change: A pan heating up on the stove top.

• Chemical

• Physical

Answer explanation

Physical Change: the molecules in the pan are speeding up, but their atoms are not rearranging.

Chemical or Physical Change: Roasting a marshmallow over a fire.

• Chemical

• Physical

Answer explanation

The molecules in the marshmallow are rearranging to form new substances as it burns.

Signs of Chemical change: Color change, new smell, light and fire produced.

Chemical or Physical Change: Baking Bread

• Chemical

• Physical

Answer explanation

The atoms in the dough are rearranging to form a baked loaf of bread.

Signs of Chemical Change: color change, new smell, new texture

Chemical or Physical Change: A banana ripens, turning from green to yellow to brown

• Chemical

• Physical

Answer explanation

Signs of Chemical Change: color change, new smell, new texture

Chemical or Physical Change: Dissolving hot chocolate mix in water

• Chemical

• Physical

Answer explanation

The hot chocolate molecules are NOT changing (their atoms are NOT rearranging). They are just dissolving (or spreading out) as they mix with the water molecules.