1. Chemical Equations Review
CH4 + 2O 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!!!

3. 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 nonmetal Li+ replaces Mg2+ and combines with Cl- The products are Mg + LiCl The balanced equation will be 2 Li + MgCl2  Mg + 2 LiCl

4. 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...

5. What am I?
Mg HCl  MgCl H2
Single replacement
Na2CO HCl  NaCl H2CO3
Double replacement
Cu S  Cu2S
Synthesis

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

7. See solubility rules Pb(NO3)2 + 2NaI  PbI2 + 2NaNO3
(aq) (aq) (s) (aq)
See solubility rules

8. Solubility Rules:

9. Net Ionic Equations Balanced 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 arrow
“Net Ionic” Equation:
Pb2+(aq) + 2I-(aq)  PbI2(s)

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

11. Net Ionic Equations Revisited:
Write the (balanced!) molecular equation first
Reaction products: swap cations and anions
Predict solubility (using Solubility rules)
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!
Write the net ionic equation next
cancel spectator ions
The net ionic equation is a “simplified” form
of the complete ionic equation

12. Balanced Molecular Equation:
Example: Problem
Balanced Molecular Equation:
Ba(NO3)2 + NiSO4

13. Balanced Molecular Equation:
Example: Problem
Balanced Molecular Equation:
Ba(NO3)2 + NiSO4
Ni(NO3)2 + BaSO4

14. Balanced Molecular Equation:
Example: Problem
Balanced Molecular Equation:
Ba(NO3)2(aq)+ NiSO4(aq)
Ni(NO3)2 (aq)+ BaSO4(s)

15. Balanced Molecular Equation:
Example: Problem
Balanced Molecular Equation:
Ba(NO3)2(aq)+ NiSO4(aq)
Ni(NO3)2 (aq)+ BaSO4(s)
Complete Ionic Equation:
Ba2+(aq) + 2NO3-(aq) + Ni2+(aq) + SO42-(aq)
Ni2+(aq) + 2NO3-(aq) + BaSO4 (s)

16. Balanced Molecular Equation:
Example: Problem
Balanced Molecular Equation:
Ba(NO3)2(aq)+ NiSO4(aq)
Ni(NO3)2 (aq)+ BaSO4(s)
Complete Ionic Equation:
Ba2+(aq) + 2NO3-(aq) + Ni2+(aq) + SO42-(aq)
Ni2+(aq) + 2NO3-(aq) + BaSO4 (s)

17. Balanced Molecular Equation:
Example: Problem
Balanced Molecular Equation:
Ba(NO3)2(aq)+ NiSO4(aq)
Ni(NO3)2 (aq)+ BaSO4(s)
Complete Ionic Equation:
Ba2+(aq) + 2NO3-(aq) + Ni2+(aq) + SO42-(aq)
Ni2+(aq) + 2NO3-(aq) + BaSO4 (s)
Net Ionic Equation:
Ba2+(aq) + SO42-(aq)
BaSO4 (s)

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

19. HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
H+(aq) + -OH(aq) H2O(l)