Drill #12

5/13, 14/2014
Write the balanced neutralization
equations for the following reactions:
1. carbonic acid & calcium hydroxide
2. potassium hydroxide and carbonic acid
3. barium hydroxide and hydrochloric acid
Drill #12

5/13, 14/2014
Write the balanced neutralization
equations for the following reactions:
1. H2CO3+CA(OH)2===> CaCO3+2H2O
2. 2KOH + H2CO3 ===> K2CO3 + 2H2O
3. Ba(OH)2 + 2HCl ===> BaCl2 + 2H2O
Objectives
SWBAT describe the concept of chemical
equilibrium and explain how and when it is
achieved.
 SWBAT write an equilibrium expression.
 SWBAT describe the progress of a chemical
reaction by using the equilibrium constant.
 SWBAT explain how physical changes such as
concentration, pressure, and temperature can
affect a chemical reaction at equilibrium.

Agenda



Equilibrium notes
Equilibrium lab
Review Worksheets
CHEMICAL
EQUILIBRIUM


Up to this point we have mostly been
considering reactions “to completion”,
where all the reactants change into
product.
However, most reactions are reversible =
occurs in both the forward and the reverse
directions.
N2(g) + 3H2(g)  2NH3 (g) forward
 N2(g) + 3H2(g)  2NH3 (g) reverse

Combined in one equation using double arrows
N2(g) + 3H2(g)  2NH3 (g)

or
N2(g) + 3H2(g) ↔ 2NH3 (g)
Chemical Equilibrium


A state in which the forward and reverse
reactions balance each other and when the
forward reaction proceeds at the same rate as
the reverse reaction.
Concentrations of reactants and products are
constant at equilibrium.
(Constant ≠ equal)
Rate vs. Time
Equilibrium Lab
Work in pairs
 Read directions first then follow directions
carefully
 Answer questions 1-4 for homework

Equilibrium constant

K is called the equilibrium constant. It is a
ratio of the concentrations of products to
the concentration of reactants.
Equilibrium Constant Expression
aA + bB ↔ cC + dD
Keq= [C]c[D]d
[A]a[B]b
A & B = molar [ ] of reactants
C & D = molar [ ] of products
Exponents a, b, c, and d = coefficients in the
balanced equation.
Equilibrium Constant


If Keq > 1: products are favored at
equilibrium
If Keq < 1: reactants are favored at
equilibrium
Important!
Only substances that are gases and
aqueous get factored into the equilibrium
expression
 Pure liquids and solids do not appear in
the expression.

Example #1

Write the equilibrium expression for the
following reaction:
2 CO (g) + O2 (g) ↔ 2 CO2 (g)
Answer

Keq = [CO2]2 / ([CO]2[O2])
Example #2

Write the equilibrium expression for the
following reaction:
CO (g) + 3 H2 (g) ↔ CH4 (g) + H2O (g)
Answer

Keq = [CH4][H2O] / ([CO][H2]3)
Assignment

Complete Equilibrium Constant WS – #1-5
Drill #13


5/15, 19/2014
What is the pH of a 2.23 x 10-6 M
solution of HI?
What is the pH and pOH of a 2.34 x 105 M NaOH solution?
Drill #13


5/15, 19/2014
What is the pH of a 2.23 x 10-6 M solution
of HI? Ans: pH = 5.65
What is the pH and pOH of a 2.34 x 10-5
M NaOH solution? Ans: pOH = 4.63,
pH = 9.38
Agenda


Acids and Bases Test
Le Chatelier Principle
Homework

Le Chatelier’s Worksheet (given to you last class)
Homework Due:
Bean Lab
 Equilibrium Constant WS

Important! Changes to Test
7. In the titration of a solution of Sr(OH)2 with HCl, the mole
ratio of base to acid
a.) is 1:1
c.) is 2:1
b.) is 1:2
d.) cannot be determined
10. An Arrhenius acid is a(an)
a.) a substance that reacts with a salt.
b.) substance that donates a H+ ion when combined with
a base.
c.) substance that releases H+ ions in an aqueous solution.
d.) substance that releases OH- ions in a aqueous
solution.
LE CHÂTELIER’S
PRINCIPLE
Question
Can we change the equilibrium position
thereby increasing the amount of products
in a reaction?
 Yes – by adding stress to a system in
equilibrium.

Le Châtelier’s Principle


If a stress is applied to a system at
equilibrium, the system shifts in the
direction that relieves the stress.
Stress is anything that upsets equilibrium –
changes in concentration, pressure, or
temperature.
Concentration
Measure of molarity (moles/L)
 If you ↑concentration of a reactant,
equilibrium will shift toward the products.
 If you ↓concentration of a reactant,
equilibrium will shift toward the reactants.

• CO(g) + 3H2(g) ↔ CH4(g) + H2O(g)
CO(g)
• CO(g) + 3H2(g) ↔ CH4(g) + H2O(g)
• CO(g) + 3H2(g) ↔ CH4(g) + H2O(g)
• CO(g) + 3H2(g) ↔ CH4(g) + H2O(g)
H2O(g)
Changes in Concentration
A + B <=> C + D
• Increasing the concentration of “A” will
shift the reaction to the right
– we need to get rid of excess “A”
• Decreasing the concentration of “C”
will shift the reaction to the right
– there is a deficit, so more “C” needs to be
made
Temperature
• Increasing the temperature shifts
the reaction away from the side
that contains the “heat”
• Decreasing the temperature shifts
the reaction toward the side that
contains the “heat”
Temperature
• Think of heat as a reactant or a
product.
CO(g) + 3H2(g) ↔ CH4(g) + H2O(g) +
heat
Is this Exothermic or Endothermic?
CO(g) + 3H2(g) ↔ CH4(g) + H2O(g) + heat
heat
CO(g) + 3H2(g) ↔ CH4(g) + H2O(g) + heat
Sample Reaction
heat + NH4Cl (s) <=> NH3 (g) + HCl (g)
• In the above endothermic reaction,
increasing the temperature will
drive the reaction to the right (in
other words, forward)
Pressure
• Ideal Gas Law: PV=nRT
• If ↑P then ↑n, which means more
number of atoms.
• If ↑P, then the equilibrium will shift
toward the side with fewer moles
of gas.
• CO(g) + 3H2(g) ↔ CH4(g) + H2O(g)
4 moles of gas
2 moles of gas
Note: If moles of gaseous reactant =
moles of gaseous product, then no shift in
equilibrium will occur from a change in
pressure
Le Châtelier’s Principle
• If a stress is applied to a
system at equilibrium, the
system shifts in the direction
that relieves the stress.
– Concentration
Note: Only temperature
– Pressure
affects K. The larger
– Temperature the value of K, the more
product at equilibrium.
Assignment
• Le Châtelier’s Principle Worksheet
Wrap up


If Keq > 1:
equilibrium
are favored at
If Keq < 1:
equilibrium
are favored at
Drill #14


May 19 & 20, 2014
What are the 3 types of stress that can affect the
equilibrium of a system?
Which states of matter get factored into an
equilibrium expression?
Agenda
Go over Equilibrium Worksheet
 Notes on Equilibrium Problems
 Complete the following worksheets:

16-3 Review and Reinforcement
 2 – Equilibrium Worksheets handed out to you by
sub

Announcement!!

Wear closed-toed shoes next
class. We will be in the lab!
DIFFERENT TYPES OF
EQUILIBRIUM
Concentration Equilibrium Kc (or Keq)


nA + mB ↔ xC + yD
Kc = [C]x[D]y
[A]n[B]m

Remember…equilibrium is where the rates of
forward and reverse reactions are the same. It
means that the concentrations do not change, NOT
that they are identical.

Because equilibrium expressions have to do with
concentration (in molarity) we do not include items
that are not in solution so NO LIQUID or SOLID
states! They are in excess so can be ignored.
Acid Equilibrium

Acid + H2O ↔ H3O+ + Acid Ion
or HA + H2O ↔ H3O+ + A-
Ka = [H3O+][A-]
[HA][H2O]
Ka = [H3O+][A-]
[HA]
Because water is a solvent and its conc. greatly
exceeds the acid, we can assume that the conc. of
water does not change.
Base Equilibrium

Base + H2O ↔ OH- + Base Ion
or B + H2O ↔ OH- + HB+
Kb = [OH-][HB+]
[B][H2O]
Kb =
[OH-][HB+]
[B]
Property
Ka value
Position of
equilibrium
Strong Acid
Ka is large
Far to the right
(a lot of
dissociation)
[H+] compared [H+]≈[HA]o
to original
[HA]
Strength of
A- is much
conjugate
weaker
base
Weak Acid
Ka is small
Far to the left
(little
dissociation)
[H+]<<[HA]o
A- is much
stronger
Graphic Representation of
the Behavior of Acids of
Different Strengths in
Aqueous Solution
Solubility Equilibrium


Salt (s) ↔ Cation (aq) + Anion (aq)
Solids are not included in equilibrium equations!
So…
Ksp = [Cation][Anion]
Solubility Equilibrium Example



CaF2 (s) ↔ Ca+2 (aq) + 2F- (aq)
Solids are not included in equilibrium equations!
So…
Ksp = [Ca+2][F-]2

Write the equilibrium expression for the
reaction:
H2 (g) + I2 (s)  2HI (g)
Keq = [HI]2
[H2]

a)
b)
c)
d)
How would the following shift the equilibrium in the
equation (forward, reverse or no change):
H+ (aq) + Cl- (aq) ↔ HCl (aq) + 10.3 kJ
Increasing temperature
Decreasing pressure
Adding NaCl
Adding NaOH