Chemthink; Chemical Reactions

1. The starting materials in a reaction are called reactants.
2. The ending materials in a chemical reaction are called products.
3. The arrow indicates a chemical reaction has taken place.
4. All reaction have one thing in common: there is a rearrangement of chemical bonds.
5. Chemical reactions always involve breaking old bonds, forming new bonds, or both.
6. In all reaction we still have all of the atoms at the end that we had at the start.
7. In every reaction there can never be any missing atoms or new atoms.
8. Chemical reactions only rearrange the bonds in the atoms that are already there.
9. If we use only atoms shown, we’d have 2 atoms of H and 2 atoms of O as reactants.  This would make 1 molecule of H2O, but we’d have 1 atom of O leftover. However, this reaction only makes H2O.
10. 1 H2 + 1 O2 = 1 H2O

Which is the same as:

# of atoms               # of atoms

in Reactants              in Products

2                     H                         2

2                     O                         1

11. This idea is called the Law of Conservation of Mass.
12. There must be the same type of atoms and the same number of atoms before the reaction and after the reaction.
13. The balanced equation for this reaction is: 2 Cu + 1 O2 = 2 CuO
14.  In the unbalanced equation there are:
15. Reactants:            Products:
    Cu atoms 1                Cu atoms 1
    O atoms   2                O atoms   1
16. 15.  To balance the equation, we have to add 1 molecule to the products, because this reaction doesn’t make lone O atoms to the reactants.
    16.  When we added a molecule of CuO, now the number lf O atoms is balanced but the number of  Cu atoms don’t match.  Now we have to add more Cu atoms to the reactants.
    17.  The balanced equation for this reaction is:
    2 Cu + 1 O2 = 2 CuO
      This is the same thing as saying:
                Reactants                        Products
                Cu atoms 2                        Cu atoms  2
                O atoms   2                        O atoms    2
          18. The balanced equation for this reaction is:
                 1 CH4 + 2 O2 = 2 H2O + 1 CO2
    
    
    19. The balanced equation for this reaction is:
           1 N2 + 3 H2 = 2 NH3
    
    
    20. The balanced equation for this reaction is:
           2 KCIO3 = 2 KCI + 3 O2
    
    
    21.  The balanced equation for this reaction is:
    4 AI + 3 O2 = 2 AI2O3
    
    
    Summary
    
    
    1. Chemical reactions always involve breaking bonds, making bonds, or both.
    2. The Law of Conservation of Mass says that the same atoms must be present before and after the reaction.
    3. To balance a chemical equation, you change the coefficients in front of each substance until there are the same number of each type of atom in both reactants and products.