Chemical Reaction
Equations
Section 7.1 pg. 278-285
Reaction Assumptions
Reactions are spontaneous – reactions will occur when all
the reactants are mixed together
Reactions are fast – the reaction must occur within a
reasonable time (see pg. 280)
Reactions are quantitative – one that is more than 99%
complete; in other words, at least one reactant is
completely used up
Reactions are stoichiometric – means that there is a
simple whole-number ratio of chemical amounts of
reactants and products (the coefficients for a balanced
equation do not change)
Net Ionic Equations
A chemical reaction equation that includes only reacting entities
(molecules, atoms and/or ions) and omits any that do not change
Writing Net Ionic Equations:
1) Write a complete balanced chemical equation
2) Dissociate all high-solubility ionic compounds, and ionize all
strong acids to show the complete ionic equation
3) Cancel identical entities that appear on both the reactant and
product sides
4) Write the net ionic equation, reducing coefficients if
neccessary
When cancelling spectator ions,
they must be identical in every way:
chemical amount, form (atom, ion,
molecule) and state of matter
Practice
Write the net ionic equation for the reaction of aqueous barium chloride and
aqueous sodium sulfate. (Refer to the solubility table)
1) BaCl2(aq) + Na2SO4(aq)  BaSO4(s) + 2NaCl(aq)
2) Ba2+(aq) + 2Cl-(aq) +2Na+(aq) + SO42-(aq)  BaSO4(s) + 2Na+(aq) + 2Cl-(aq)
(Complete ionic equation)
3) Ba2+(aq) + 2Cl-(aq) +2Na+(aq) + SO42-(aq)  BaSO4(s) + 2Na+(aq) + 2Cl-(aq)
4) Ba2+(aq)) + SO42-(aq)  BaSO4(s) (Net ionic equation)
Ions that are present but do not take part in (change during) a reaction are
called spectator ions (like spectators at a sports game: they are present but
do not take part in the game)
Practice
Write the net ionic equation for the reaction of zinc metal and aqueous
copper (II) sulfate (Refer to the solubility table)
1) Zn(s) + CuSO4(aq)  Cu(s) + ZnSO4(aq)
2) Zn(s) + Cu2+(aq) + SO42-(aq)  Cu(s) + Zn2+(aq) + SO42-(aq)
(Complete ionic equation)
3) Zn(s) + Cu2+(aq) + SO42-(aq)  Cu(s) + Zn2+(aq) + SO42-(aq)
4) Zn(s) + Cu2+(aq)  Cu(s) + Zn2+(aq) (Net ionic equation)
For entities involving strong
acids, H+(aq) is used as a matter
of convenience over H3O+(aq)
Practice
Write the net ionic equation for the reaction of hydrochloric acid and
barium hydroxide
1) 2HCl(aq) + Ba(OH)2(aq)  BaCl2(aq) + 2HOH(l)
aka: 2H2O(l)
2) 2H+(aq) + 2Cl-(aq) + Ba2+(aq) + 2OH-(aq)  Ba2+(aq) + 2Cl-(aq) + 2H2O(l)
(Complete ionic equation)
3) 2H+(aq) + 2Cl-(aq) + Ba2+(aq) + 2OH-(aq)  Ba2+(aq) + 2Cl-(aq) + 2H2O(l)
4) H+(aq)) + OH-(aq)  H2O(l) (Net ionic equation) – coefficients reduced to 1
Limiting and Excess Reagents
Cu(s) + AgNO3(aq) 
What is in the container when the reaction is finished?
 Cu(NO3)2(aq) + Ag(s)
(Cu2+(aq) = blue)
But how do you know the reaction is done?? There is still copper left!
(a) Copper wire and a beaker with aqueous silver nitrate solution
(b) A few moments after the wire is immersed
(c) The beaker contents after 24 h
Limiting and Excess Reagents
When no further changes appear to be occurring, we assume that all of the
AgNO3(aq) that was initially present has now been completely reacted.
A limiting reagent is the reactant whose entities are completely consumed in a
reaction, meaning the reaction stops.
In order to make sure this happens, more of the other reactant must be
present than is required
An excess reagent is the reactant whose entities are present in surplus amounts,
so that some remain after the reaction ends..
In our reaction: much more copper was used than
needed (evidenced by the unreacted copper) so we
assume the reaction ended when no more silver ions
were left, so silver nitrate was the limiting reagent.
Homework:
Net Ionic Worksheet
Pg.284 #10-14
Pg. 285 #3-7