Reactants General reaction equation: Products Bricks + lumber + cementBuilding

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 Chlorine gas is actually diatomic. Its formula is Cl 2. The other diatomic elements are H 2, N 2, O 2, F 2, Br 2, I 2

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.

____ 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.

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 + ____ Pb(NO 3 ) 2 ____ Zn(NO 3 ) 2 + ____ Pb 1 Zn 1 Pb 1 Zn R P 1 Pb 1 NO 3 This reaction equation is already balanced! STOP

2)Solid aluminum bromide and dichlorine gas react to form solid aluminum chloride and dibromine gas. ____ AlBr 3 + ____ Cl 2 ____ AlCl 3 + ____ Br 2 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

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 3 Na herePut a 3 here 3 Six H total this side 1 st pass: 2 nd pass:Put a 3 here 3 3 rd pass:One phosphate and 3 O this side

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