Chemical Equations Review

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 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 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 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 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 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 the reaction: HCl(aq) + NaOH(aq) ?

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

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