Topic: Names, Formulas, Equations, & Reactions Aim: How do we balance chemical equations? Do now: List the number of each element present in the following compound: 3(NH4)3PO4 HW:

REACTANTS YIELD PRODUCTS Chemical Equations Show which bonds are broken and which bonds are built # of atoms on left side of arrow MUST equal # of atoms on the right side of arrow REACTANTS YIELD PRODUCTS Mg + 2HCl  MgCl2 + H2 1 Mg, 2 H, 2 Cl 1Mg, 2 H, 2 Cl

Hint:

Examples Unbalanced Equation Balanced Equation Al + O2  Al2O3 1 Al on left 2 Al on right 2 O on left 3 O on right Balanced Equation 4Al + 3O2  2Al2O3 4 Al on left 4 Al on right 6 O on left 6 O on right

How do we balance equations? Change the COEFFICIENTS of the formulas until you have the same # of atoms on both sides of arrow NEVER change a subscript!! EVER!

Balancing Equations __ H2 + __ O2  __ H2O 2 H 2 H 2 O 1 O Starting #s 2 O 1 O __ H2 + __ O2  2 H2O 2 H 4 H Update #s 2 O 2 O 2 H2 + __ O2  2 H2O 4 H 4 H Update #s 2 O 2 O

Balancing Equations __C + __H2  __C3H8 1 C 3 C 8 H 2 H Starting #s 8 H 2 H 3C + 4H2  __C3H8 3 C 3 C Updated #s 8 H 8 H

More Practice. Because I care. N2 + O2  N2O K + Br2  KBr

Still caring… Al + HCl  H2 + AlCl3

How can one person care so much? If a polyatomic ion is present in the equation ON BOTH SIDES, keep it together as a unit. (It’s easier to balance.) BaCl2 + Al2(SO4)3  BaSO4 + AlCl3

If you see OH on one side and H2O on the other, rewrite H2O as HOH so you now have an OH on each side. Al(OH)3 + H2SO4  Al2(SO4)3 + H2O