1. Reactants General reaction equation: Products Bricks + lumber + cementBuilding

2. Law of conservation of mass: matter is neither created nor destroyed during a physical or chemical change or….What goes in must come out. Ex: 23 g of sodium metal is reacted with 35 g of chlorine gas to form sodium chloride. How much sodium chloride was formed? 23 g Na (s) + 35 g chlorine (g)58 g of NaCl reactantsproducts Remember  Chlorine gas is actually diatomic. Its formula is Cl 2. Can you remember the other diatomic elements? H 2, N 2, O 2, F 2, Br 2, I 2

3. Let’s look at that reaction again… Na + Cl 2 NaCl Imagine that we’re reacting atoms Na Cl + Na Cl Na 2 Na + Cl 2 2 NaCl Now the reaction is balanced.

4. ____ H 2 + ____ O 2 ____ H 2 O 2 H 2 O 2 H R P 1 O2 x 2 = 2 O = 4 H 2 x = 4 H 2 The large numbers in front of the chemical formulas are called coefficients. They act like multipliers when balancing equations.

5. 1)Zinc metal and an aqueous solution of lead(II) nitrate react to form an aqueous solution of zinc(II) nitrate and lead metal. __ Zn (s) + __ Pb(NO 3 ) 2 (aq)__ Zn(NO 3 ) 2 (aq) + __ Pb (s) 1 Zn 1 Pb 1 Zn R P 1 Pb 1 NO 3 This reaction equation is already balanced! STOP Zn(s)+Pb 2+ NO 3 1- (aq)  Zn 2+ NO 3 1- Pb(s) +

6. 2)Solid aluminum bromide and chlorine gas react to form solid aluminum chloride and bromine liquid. ___ AlBr 3 (s) + ___ Cl 2 (g)___ AlCl 3 (s) + ___ Br 2 (l) 1 Al 3 Br 1 Al R P 2 Br 2 Cl3 Cl 2 x = 6 Br3 x= 6 Br 23 2 x = 2 Al 2 x = 2 Al 2 2 x= 6 Cl3 x= 6 Cl 3 This reaction equation is balanced! STOP (s)Al 3+ Br 1- +Cl 2 (g)  (s)Al 3+ Cl 1- +Br 2 (l)

7. An alternative balancing technique: Balancing by inspection Phosphoric acid and sodium hydroxide react to form water and sodium phosphate. ____H 3 PO 4 + ____ NaOH____H 2 O + ____Na 3 PO 4 2 nd pass: Balance non-phosphate oxygens (phosphates are already balanced) 3 rd pass: Check hydrogens 1 st pass: Balance sodiums PO 4 3- H+H+ Na 1+ OH 1-  H2OH2O Na 1+ PO 4 3- 3 3 (3 on both sides) (6 H on both sides) (3 on both sides) + +

8. Balance the following by inspection: 1. ___C 2 H 4 + ___O 2  ___CO 2 + ___H 2 O Balance carbons 2 Balance hydrogens 2 Balance oxygens 3 2. ___P + ___O 2  ___P 2 O 5 Balance oxygens Balance phosphorus 254