Chemical Reactions

Molecules are made up of atoms connected together.

In solids, molecules are packed closely together. In gases, molecules are spread far apart.

You can cause substances to change state by adding energy, most often thermal energy (heat).

Ice melting and turning into liquid and water boiling and evaporating into a gas. Any instance of melting or freezing would be considered a phase change.

When ice melts, the solid turns into a liquid. When you burn something, energy causes an old substance to change into a new substance.

It is a chemical change because your saliva causes a chemical reaction and new substances are formed.

In a physical change, no new substances are formed. In a chemical change, new substances are formed.

If a new substance is formed, it has different properties.

Steel wool burning, which causes the iron to combine with oxygen and form iron oxide.

By testing the properties before and after the reaction. Iron is flammable and will light on fire when touched with a battery. After combining with oxygen, it is no longer flammable because the properties have changed.

Magnetism, flammability, electricity, density, and odor

A catalyst helps the chemical reaction happen faster, but it does not become a part of the new substance.