Chemical Reactions

• Chemical changes and physical changes are both changes that are often seen in chemistry.
• Physical changes

  A physical change occurs when a substance changes without becoming a new chemical.

  Physical changes are often changes in state such as melting, freezing, boiling, condensing and dissolving.
• Chemical changes

  A chemical change happens when the atoms present in a reactant is rearranged to form one or more products.

  Chemical reactions are processes that bring about chemical change.
• Signs of chemical change:

  A change in temperature

  A change in colour

  Formation of a gas

  Formation of a solid
• Exothermic reactions are reactions that give out heat.
• Endothermic reactions are reactions that absorb heat from the surroundings.
• Chemical changes are irreversible but physical changes are reversible.