5.4 Flashcards
1
Q
Reactions Not at Equilibrium
A
2
Q
•For the reaction conditions shown;
A
3
Q
Concentration (M)
A
4
Q
equilibrium is not reached until NO
A
concentration
5
Q
reaches 0.0125 mol/L
A
6
Q
0.08
A
7
Q
0.06
A
8
Q
0.04
A
9
Q
0.02
A
10
Q
line
A
11
Q
Time
A
12
Q
(a)
A
13
Q
Chemical
A
14
Q
Equilibrium
A
15
Q
N
A
o
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Q
NO.
A
17
Q
2NO
A
18
Q
P2 (3)
A
19
Q
0.08
A
20
Q
0.06
A
21
Q
0.04
A
22
Q
The Reaction Quotient
A
Q
23
Q
Keg
A
24
Q
0.02
A
25
eq
26
0
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Q-lT[D
28
[A|[B
29
Time
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(bl
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Chemical
32
•Reaction quotient (Q): a numerical value
33
determined by using the same formula as the
34
equilibrium constant (using data for a reversible
35
reaction) that may or may not be at equilibrium.
36
For: aA + bB cC + dD:
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3-4/ 20
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NO
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Determining the Direction of a Reaction
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NO
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•The symbols forQ and K are placed on a number
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•The reaction will move in the direction from Q to K.
43
eg
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Determining the Direction of a Reaction
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Q>K:
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Determining the Direction ofa Rea( 67 /20
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ratio of products
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to reactants is
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too large
50
reaction will
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proceed LEFT to
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reach
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equilibrium.
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Q=
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[products]
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[reactants]
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Reaction proceeds
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toward right
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forming products
60
Example 1:
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eqilitriur is
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Q> K
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net reaction to left
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Reactions Not at Equl lilbrium
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ui
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The Reaction Quotlent
C
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•Reaxtion ouotiernt (Q) a numerical value
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using the sane torry
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Q=
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uil NO
:6centretion
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tormuls zs the
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raactlcnl that may or may nat be at equi lari am.
73
erminlng the Dlrectlon of a Reaction
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K
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Q=K:
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Qand K
are olkced ur a uribe
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raler wll mnes in the cirertiar fon Qto K
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the system is at
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equilibrium.
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K= Q=
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[products]
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[reactants]
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Q= K
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Reaction proceeds
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toward left
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forming reactants
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no net reaction
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Q
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Determining the Direction of a Reaction
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ratio of products
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Calculate Q to determine the direction of reaction when
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the concentrations are: [CH
]=0.100 M
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M
[H
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AAnilibciun constant for the reaction below is 5.67.
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to reactants is to0
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small
reaction
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will proceed
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RIGHT to reach
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equilibrium.
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Q=
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[products]
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[reactants]
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Q
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net reaction to right
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CHạ (e) + H
O) Coig + 3H2()
106
Example 2:
107
Determining the direction of a Reaction
108
In the Haber process for manufacturing ammonia
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nitrogen and hydrogen combine in the presence of a
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catalyst:
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Nzte) + 3H (a) 2NHa (e)
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At 300 °C
the value of K._ for this reaction is 7.3.
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eq
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The following concentrations of gases are present in
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a container at 300°C: [N
] = 0.10 mol/L
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mol/L
and [NH
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gases at equilibrium? If not
in which direction will
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the reaction go to reach equilibrium?
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Example 3: Calculating Equilibrium
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Concentrations from Initial Concentration
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Carbon monoxide reacts with water vapour to
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produce carbon dioxide and hydrogen. At 900 °d
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K = 4.200. Calculate the concentrations of all
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entities at equilibrium if 4.000 mol of each entity
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are initially placed in a 1.000 L closed container.
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eo
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Step 1: Calculate concentrations given c=nv
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Step 2: Calculate the value of Q
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Example 3 Continued
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Step 3: Set up an ICE chart
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Determining the Direction of a Reactinn
132
ERample
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Initial conc. (mol/L)
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Determining the Direction of a
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pTcHad LEFT
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ceullbdurh.
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|Change in conc. (mol/4)
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ratio of aradu.cti tha systam Is at rato of praeucts
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snall reacrior
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BISHT OrE8th
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ing the Direction af a neaction
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M. EH
O| 0.200 M and J]=0200 M
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onc.
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co(g)
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4
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= 4.000 mol/1.000 L
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= 4.000 M
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blve for X
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Q = [C0
][H
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= (4.000)(4.000)/(4.000)(4.
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= 1.000.. NOT at equilibril
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+ H
ole)
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4
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co
(e)
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4
156
H
(e)
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4
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Step 1. Write the balanced equation for the reaction.
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Step 2. Under the balanced equation
make a table that lists for each substance
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involved in the reaction:
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(a) The initial concentration
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the
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(b) The change in concentration on going to equilibrium
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(c) The equilibrium concentration
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In constructing the table
define x as the concentration (mol/L) of one of
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he substances that reacts on going to equilibrium
then use the
167
stoichiometry of the reaction to determine the concentrations of the other
168
substances in terms of x.
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Step 3. Substitute the equilibrium concentrations into the equilibrium equation for
170
the reaction and solve for x. If you must solve a quadratic equation
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choose the mathematical solution that makes chemical sense.
172
Step 4. Calculate the equilibrium concentrations from the calculated value of x.
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Example 4
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Step 5. Check your results by substituting them into the equilibrium equation.
175
Calculations with Imperfect Squares
176
•The "thousand rule" is an assumption made to
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simplify problems:
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If the ratio of:
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[initial concentration of reactant]/Keq> 1000
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then x is very small compared to initial
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concentration
so it is considered negligible with
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respect to the change from the initial
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concentration
and x may be removed from that
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part of the calculation.
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**Note: this is nota great rule
but acceptable for high school
186
chemistry
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Carbon monoxide is a primary starting material in the
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synthesis of many organic compounds
including
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methanol
CH
190
13-14/ 20
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At 2000°C
K is 6.40 x 10 for the decomposition of
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carbon dioxide into carbon monoxide and oxygen.
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Calculate the concentrations of all entities at
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equilibrium if 0.250 mol/L of COo
lel is placed in a
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closed container and heated to 2000 °C.
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2C02 (8)
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* 2C0e + Oz(e)
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