Chemical Equations ReviewCH4 + 2O2 CO2 + 2H2O

“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 + MgCl2 ???????

Single replacement reaction. Why?Li is a metal, Mg is a metal, Cl is a nonmetalLi+ replaces Mg2+ and combines with Cl-

The products are Mg + LiCl The balanced equation will be2 Li + MgCl2 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 MgCl2 + H2

Single replacement

Na2CO3 + HCl NaCl + H2CO3

Double replacement

Cu + S Cu2S Synthesis

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

(aq) + Cl-

(aq)

Pb(NO3)2 + 2NaI PbI2 + 2NaNO3

(aq) (aq) (s) (aq)

See solubility rules

Solubility Rules:

Net Ionic EquationsBalanced Chemical Equation:

Pb(NO3)2(aq) + 2NaI(aq) PbI2(s) + 2NaNO3(aq)

“Complete Ionic” Equation:Pb2+

(aq) + 2NO3-(aq) + 2Na+

(aq)+ 2I-(aq) PbI2(s) + 2Na+

(aq) + 2NO3- (aq)

Cancel the “spectator ions” that appear on both sides of the arrowPb2+

(aq) + 2NO3-(aq) + 2Na+

(aq)+ 2I-(aq) PbI2(s) + 2Na+

(aq) + 2NO3- (aq)

“Net Ionic” Equation:Pb2+

(aq) + 2I-(aq) PbI2(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 ionizeion subscripts in the molecular equation become

coefficients in the complete ionic equation!3) Write the net ionic equation next

- cancel spectator ionsThe net ionic equation is a “simplified” form of the complete ionic equation

Example: Problem

Ba(NO3)2 + NiSO4

Balanced Molecular Equation:

Ba(NO3)2 + NiSO4 Ni(NO3)2 + BaSO4

Balanced Molecular Equation:

Example: Problem

Ba(NO3)2(aq)+ NiSO4(aq) Ni(NO3)2 (aq)+ BaSO4(s)

Balanced Molecular Equation:

Example: Problem

Ba2+(aq) + 2NO3

-(aq) + Ni2+

(aq) + SO42-

(aq)

Ni2+(aq) + 2NO3

-(aq) + BaSO4 (s)

Balanced Molecular Equation:

Complete Ionic Equation:

Example: Problem

Ba(NO3)2(aq)+ NiSO4(aq) Ni(NO3)2 (aq)+ BaSO4(s)

Ba2+(aq) + 2NO3

-(aq) + Ni2+

(aq) + SO42-

(aq)

Ni2+(aq) + 2NO3

-(aq) + BaSO4 (s)

Balanced Molecular Equation:

Complete Ionic Equation:

Example: Problem

Ba(NO3)2(aq)+ NiSO4(aq) Ni(NO3)2 (aq)+ BaSO4(s)

Ba2+(aq) + 2NO3

-(aq) + Ni2+

(aq) + SO42-

(aq)

Ni2+(aq) + 2NO3

-(aq) + BaSO4 (s)

Balanced Molecular Equation:

Complete Ionic Equation:

Example: Problem

Ba(NO3)2(aq)+ NiSO4(aq) Ni(NO3)2 (aq)+ BaSO4(s)

Net Ionic Equation:Ba2+

(aq) + SO42-

(aq) BaSO4 (s)

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

HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)

H+(aq) + -OH(aq) H2O(l)