Chemical Equations Review CH 4 + 2O 2 CO 2 + 2H 2 O “coefficients”“subscripts” coefficients can be changed to achieve mass balance but subscripts are never changed to balance an equation Why? Because changing a subscript changes the compound entirely!!!

So how do we get subscripts? In ionic compounds you simply cross the ions charge values. Li + MgCl 2  ??????? Single replacement reaction. Why? Li is a metal, Mg is a metal, Cl is a nonmetal Li + replaces Mg 2+ and combines with Cl - The products are Mg + LiCl The balanced equation will be 2 Li + MgCl 2  Mg + 2 LiCl

Balancing a Chemical Equation write formula for each reactant and product on the correct side of the “reaction arrow” count atoms of each element on both sides of arrow start with the compound which has the most complex formula add coefficients to chemical formulas to balance numbers of each atom trial and error begins...

What am I? Mg + HCl  MgCl 2 + H 2 Single replacement Na 2 CO 3 + HCl  NaCl + H 2 CO 3 Double replacement Cu + S  Cu 2 S Synthesis

NaCl is soluble in water. Solid NaCl dissociates into Na + and Cl - ions in aqueous solution: NaCl (s)  Na + (aq) + Cl - (aq)

Pb(NO 3 ) 2 + 2NaI  PbI 2 + 2NaNO 3 (aq) (aq) (s) (aq) See solubility rules

Solubility Rules:

Net Ionic Equations Balanced Chemical Equation: Pb(NO 3 ) 2 (aq) + 2NaI (aq)  PbI 2 (s) + 2NaNO 3 (aq) “Complete Ionic” Equation: Pb 2+ (aq) + 2NO 3 - (aq) + 2Na + (aq) + 2I - (aq)  PbI 2 (s) + 2Na + (aq) + 2NO 3 - (aq) Cancel the “spectator ions” that appear on both sides of the arrow Pb 2+ (aq) + 2NO 3 - (aq) + 2Na + (aq) + 2I - (aq)  PbI 2 (s) + 2Na + (aq) + 2NO 3 - (aq) “Net Ionic” Equation: Pb 2+ (aq) + 2I - (aq)  PbI 2 (s)

For the exam: know how to use solubility rules to predict whether an ionic compound is insoluble or not

Net Ionic Equations Revisited: 1)Write the (balanced!) molecular equation first -Reaction products: swap cations and anions -Predict solubility (using Solubility rules) 2)Write the complete ionic equation next -(s) compounds don’t ionize -(aq) compounds do ionize ion subscripts in the molecular equation become coefficients in the complete ionic equation! 3)Write the net ionic equation next -cancel spectator ions The net ionic equation is a “simplified” form of the complete ionic equation

Example: Problem Ba(NO 3 ) 2 + NiSO 4 Balanced Molecular Equation:

Ba(NO 3 ) 2 + NiSO 4 Ni(NO 3 ) 2 + BaSO 4 Balanced Molecular Equation: Example: Problem

Ba(NO 3 ) 2(aq) + NiSO 4(aq) Ni(NO 3 ) 2 (aq) + BaSO 4(s) Balanced Molecular Equation: Example: Problem

Ba 2+ (aq) + 2NO 3 - (aq) + Ni 2+ (aq) + SO 4 2- (aq) Ni 2+ (aq) + 2NO 3 - (aq) + BaSO 4 (s) Balanced Molecular Equation: Complete Ionic Equation: Example: Problem Ba(NO 3 ) 2(aq) + NiSO 4(aq) Ni(NO 3 ) 2 (aq) + BaSO 4(s)

Ba 2+ (aq) + 2NO 3 - (aq) + Ni 2+ (aq) + SO 4 2- (aq) Ni 2+ (aq) + 2NO 3 - (aq) + BaSO 4 (s) Balanced Molecular Equation: Complete Ionic Equation: Example: Problem Ba(NO 3 ) 2(aq) + NiSO 4(aq) Ni(NO 3 ) 2 (aq) + BaSO 4(s)

Ba 2+ (aq) + 2NO 3 - (aq) + Ni 2+ (aq) + SO 4 2- (aq) Ni 2+ (aq) + 2NO 3 - (aq) + BaSO 4 (s) Balanced Molecular Equation: Complete Ionic Equation: Example: Problem Ba(NO 3 ) 2(aq) + NiSO 4(aq) Ni(NO 3 ) 2 (aq) + BaSO 4(s) Net Ionic Equation: Ba 2+ (aq) + SO 4 2- (aq) BaSO 4 (s)

What is the Net Ionic Equation for the reaction: HCl (aq) + NaOH (aq) ?

HCl (aq) + NaOH (aq) H 2 O (l) + NaCl (aq) H + (aq) + - OH (aq) H 2 O (l)