Chemical Equations Review
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So how do we get subscripts?
In ionic compounds you simply cross the ionscharge 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
Balancing a Chemical Equation
•write formula for each reactant and producton the correct side of the “reaction arrow”
•count atoms of each element on both sidesof arrow
•start with the compound which has the mostcomplex formula
•add coefficients to chemical formulas tobalance 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 solublein water. SolidNaCl dissociatesinto Na+ and Cl-ions in aqueoussolution:
NaCl(s) Na+(aq) + Cl-(aq)
Pb(NO3)2 + 2NaI PbI2 + 2NaNO3
(aq) (aq) (s) (aq)
See solubility rules
Solubility Rules:
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
Pb2+(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 predictwhether 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 becomecoefficients 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(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 thereaction: HCl(aq) + NaOH(aq) ?
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
H+(aq) + -OH(aq) H2O(l)