CHEMICAL EQUATIONS BY MS. PACHECO

RECALL… The law of conservation of matter: Matter can neither be created nor destroyed in a chemical reaction.

Therefore… The number of atoms of each element must remain the same before and after a chemical reaction. To do this, you BALANCE the equation.

To balance an equation… You may use COEFFICIENTS only (Numbers written before a formula)

For example… Ca + O2  CaO left side right side Ca=1 Ca =1 O=2 O=1

To balance the equation… Ca + O2  CaO You need to increase the number of oxygens on the right. Remember that you can only use COEFFICIENTS!!

Ca + O2  CaO Ca + O2  2CaO Add a 2 in front of the CaO on the right. Left side Right side Ca=1 Ca=2 O=2 O=2 The O’s balance, but now the Ca’s are off!!

Ca + O2  2CaO Now, add a 2 in front of the Ca on the left. 2Ca + O2  2CaO Left side right side Ca=2 Ca=2 O=2 O=2 The equation is balanced and the law of conservation of matter is satisfied!!!!

Now your turn… Balance the following equation. Remember to use coefficients only!!! Al + F2  AlF3

Al + 3F2  2AlF3 Then, balance the Al’s 2Al + 3F2  2AlF3 HINT: Odd-even rule Al + 3F2  2AlF3 Then, balance the Al’s 2Al + 3F2  2AlF3

Also… Complete chemical equations use letters after the formulas to represent the state of the compound. (s) for solid (l) for liquid (g) for gas

Example… Na + Cl2NaCl Na is a solid Cl2 is gas NaCl is a solid So… Na(s) + Cl2(g)NaCl(s)

Lastly… Diatomic elements: When the following elements are BY THEMSELVES (not part of a compound), they combine as a pair of atoms. H2, N2, O2, F2, Cl2, Br2, I2

Example… Nitrogen gas combines with hydrogen gas to produce gaseous ammonia (NH3) N2 + H2  NH3 Don’t forget to balance!!! Include the physical state of each!!!

N2 + H2  NH3 Left side right side N=2 N=1 H=2 H=3 Use odd-even rule on H’s N2 + 3 H2  2 NH3 N=2 N=2 H=6 H=6

Include the physical state of each!!! N2 + 3 H2  2 NH3 N2(g) + 3 H2(g) 2 NH3(g)