Chemical Equilibrium
Reversible Reactions
Some reactions are said to be reversible. That
is, at the same time the reactants are
reacting to produce the products, the
products are reacting to produce the
reactants! A reversible reaction is identified
by the presence of ⇌ in a chemical
equation.
e.g. 2 H2O ⇌ H3O+ + OHNote: the concept of reversibility can also be
applied to physical changes. I.E.
Solubility: dissolving ⇌precipitation
Phase: solid ⇌liquid ⇌gas)
Dynamic Equilibrium
A reversible system is said to be in a state of
“dynamic equilibrium” when the forward
rate equals the reverse rate. In this state,
the concentration of all species remains
constant even though both the forward and
reverse processes are occurring.
The reversible system could be chemical or
physical.
Review figure 3 on page 427 and explain
what the author is trying to illustrate.
Establishment of Equilibrium
Copy and provide an explanation of the graph
in figure 6 on page 430.
Percent Reaction
• Percent Reaction is a comparison of the
yield of product at equilibrium and the
maximum possible yield which is
determined through stoichiometric
calculations.
• Percent reaction refers to the amount of
product formed or to what extent the
reaction has gone.
• Mathematically it is determined using the
formula below.
%reaction=actual yield/theor yield x 100 %
• Percent reaction is used to determine to
what extent the reaction goes in one
direction.
• If the percent reaction <1%, no reaction is
said to occur, if it is <50%, reactants are
favoured, >50%, products are favoured and
>99%, the reaction goes to completion
Tracking Concentration Changes
The most convenient method to
keep track of concentrations in
reaching equilibrium is the use
of an ICE table.
Page 428 #1,4,5
Page 437 #6,7 (top) #3,4,7-9(btm)
The Equilibrium Expressions
• For a given reaction;
aA + bB ⇌ cC + dD
K = [C]c [D]d / [A]a [B]b
• At a given temperature, this ratio
will always yield the same value
regardless of what the initial
conditions were.
• This value is called the equilibrium
constant, K.
• Only gases and aqueous solutions
are included in the equilibrium
expression as these are the only
states that have a concentration.
Magnitude of K
• The magnitude of the equilibrium constant,
K, for a reaction provides a measure of the
extent to which the reaction proceeds.
• If the value of K is much greater than 1,
than the reaction proceeds to completion
(i.e. at equilibrium the products are highly
favoured).
• If the value of K is close to one, neither
side is favoured (i.e. at equilibrium the
reactants and products are equal).
• If the value of K is much smaller than 1,
than the reaction proceeds only slightly
(i.e. at equilibrium the reactants are highly
favoured).
Page 442-47 #1-7
SECTION 7.5
Practice questions #1 – 10
Section review #1-8
Le Chatalier
tutorial worksheet equilibrium.doc
Practice Problems #1-5, 8
Section Questions #2-6
TRY THESElechatalier.doc
SOLUBILITY
As previously discussed, dynamic equilibrium exists between
the aqueous and solid forms of a solute in a saturated
mixture that contains both.
The equilibrium constant that governs this is called the
solubility product constant, Ksp.
The larger the Ksp, the more soluble the solute. Those solutes
that are defined as insoluble are those that really have a
very small Ksp. Solubility is often calculated in mol/L (of
solute).
Equation describing solubility equilibrium;
X2Y(s) ⇌2X+(aq) + Y-2(aq)
- note the stoichiometry here!
Write the Ksp expression.
Trial Ion Product, Q
If Q=Ksp then the solution is saturated.
If Q<Ksp then the solution is not saturated.
What if Q>Ksp?
SECTION 7.6 PRACTICE QUESTIONS #1-5
SECTION 7.6 SECTION QUESTIONS #4,6,8,10
WATER LAB
..\survival
kit\12Ulabs\waterlab.doc
OXALATE + CALCIUM LAB
(IN TEXT on page 517)
Chapter Review
Page 522 # 12,13,15-18
Page 523 # 10,11,13,15,16-19