5. Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept:

• a.    Students know reactant atoms and molecules interact to form products with different chemical properties.
• b.   Students know the idea of atoms explains the conservation of matter: In chemical reactions the number of atoms stays the same no matter how they are arranged, so their total mass stays the same.
• c. Students know chemical reactions usually liberate heat or absorb heat.
• d.   Students know physical processes include freezing and boiling, in which a material changes form with no chemical reaction.
• e. Students know how to determine whether a solution is acidic, basic, or neutral.