Chapter 16: Equilibrium Concept Tests
Concept Test:
Write the Kc expression for the following:
H2O(g) + CO(g)  H2(g) + CO2(g)
Kc =
4HCl(g) + O2 (g)  2H2O(g) + 2Cl2 (g)
Kc =
Concept Test:
Find the Kc for the following reaction:
N2O4 (g)  2NO2 (g)
The equilibrium concentrations for the experiment are
N2O4 = 0.0202 mole/L and NO2 = 0.00966 mole/L. Determine K
Kc =
Kc =
1
2HI(g)
Experiment Number
1
2
3
H2 (g)
Initial
Concentrations, M
[HI] = 1.000
[H2] = 0.000
[I2] = 0.000
[HI] = 0.000
[H2] = 1.000
[I2] = 1.000
[HI] = 1.000
[H2] = 1.000
[I2] = 1.000
+ I2 (g)
at 698 K
Equilibrium
Concentrations, M
[HI] = 0.786
[H2] = 0.107
[I2] = 0.107
[HI] = 1.573
[H2] = 0.213
[I2] = 0.213
[HI] = 2.360
[H2] = 0.320
[I2] = 0.320
Concept Test:
Consider the case in which the decomposition of HI(g) produces
equilibrium concentrations of H2 and I2 of 0.0250 M. Find the
equilibrium concentration of HI
Kc =
Solve for HI
HI =
Write the equilibrium expression for the following reaction:
2NO(g) + O2 (g)  2NO2 (g)
Kc = [NO2]2 = 4.67 x 1013
[NO]2[O2]
Concept Test:
Calculate the numerical value for the equation written in reverse =
2
[H2][I2]
[HI]2
0.0185
0.0183
0.0184
What if we write the reaction in terms of the formation of 1 mole of NO2?
NO(g) + ½ O2 (g)  NO2 (g)
What is the K of this reaction?
Kc = [NO2]
[NO][O2}1/2
How is THIS expression related to the original equation??
ORIGINAL EQUATION:
Kc =
[NO2]2
[NO]2[O2]
What is the Kc for the formation of 1 mole of NO2?
Kc 1 mole NO2 =
Concept Test:
Calculate the Kc expression for the following chemical reaction:
NO2 (g)  NO(g) + ½ O2 (g)
Kc =
3
Concept Test:
The reaction of steam and solid carbon produces a mixture of carbon
monoxide and hydrogen. Write the equilibrium constant expression
Kc for this reaction:
C(s) + H2O (g)  CO(g) + H2 (g)
Kc =
Concept Test:
Write the Kp expression for the following reaction:
N2 (g) + 3H2 (g)  2NH3 (g)
Kp =
From the above equation PNH3 = [NH3]RT and PN2 = [N2]RT and PH2 = [H2]RT
Concept Test:
Substitute the above relationships into the Kp expression:
Kp
=
4
Concept Test:
Given the following equation, determine Kc
H2 (g) + I2 (g)  2HI(g)
Given 1.20 M of H2 and I2 and 0.347 M HI, calculate Kc
Kc =
Kc =
Concept Test:
If the Kc value for the above reaction = 8.36 x 10-2 and the concentrations
For H2 and I2 = 0.133 M, what is the concentration of HI?
Kc =
[HI] =
5
Concept Test:
When phosgene (COCl2) , a poisonous gas that has been used as a chemical
warfare agent, is heated, it decomposes into carbon monoxide and chlorine gas
Write and balance the chemical equation!
When 2.00 moles of phosgene are put into a 1.00 L empty flask at 395oC
and allowed to come to equilibrium, the final mixture contains
0.0398 moles of chlorine. Find Kc
Remember - we need concentrations! We know the # moles and we
know the volume – calculate M
moles/
moles/
L=
M phosgene
L=
M Cl2
Make your ICE table: fill in what you KNOW
COCl2 (g)

CO(g)
I
C
E
I = initial
C = change
E = equilibrium
Kc =
6
+
Cl2 (g)
Concept Test:
You are given 0.400 moles of HI gas is placed in a 1.00 L container and allowed
to dissociate until it reaches equilibrium.
At equilibrium, its concentration is 0.0156 M
Calculate Kc
Step 1: write balanced equation
Step 2: create ICE table
Step 3: fill in values
Step 4: calculate Kc
↔
+
I
C
E
[Initial] – [Change] = [Equilibrium]
0.400 M =
M
0.400 –
=
↔
+
I
C
E
Kc =
Kc =
7
Concept Test:
When methane gas is mixed with water vapor in a 0.32 L flask,
carbon monoxide and hydrogen gas are formed at 1200 K.
At equilibrium, the flask contains 0.33 moles of CO, 0.088 moles
of H2 and 0.025 moles of CH4. What is the [H2O] at equilibrium if the
Kc = 0.33
Step 1: Write and balance the chemical reaction
Step 2: Calculate equilibrium concentrations!!
Step 3: Set-up equilibrium expression
Step 4: solve for the missing value
+
↔
+
Kc =
Kc =
concentrations:
moles CO/
moles H2/
L=
moles CH4/
L=
0.33 =
[H2O] =
[H2O] =
8
L=
M
M
M
Concept Test:
COCl2 (g) ↔ CO (g) + Cl2 (g) Kc = 8.3 x 10-4 at 360oC
Calculate the equilibrium concentrations of each species at equilibrium
in a 10.0 L flask if:
a.) 5.00 moles of COCl2 decompose
Step 1: Make sure equation is balanced
Step 2: Make an ICE table
Step 3: Calculate concentrations
Step 4: Fill in the ICE table with values
Step 5: Set-up equilibrium expression
COCl2 (g)
↔
CO (g)
+
Cl2 (g)
I
C
E
Kc =
Kc = 8.3 x 10-4 =
let’s assume that x is small. Obviously, the creation of product in
any amount is significant, but if x is small then we will not lose
a lot of starting COCl2. Kc is on the smaller side, so we will make this assumption
and see where it takes us.
How accurate is our assumption: 5% rule
Change in concentration x 100 < 5% then assumption is valid
Initial concentration
x 100 =
%
0.500
Therefore, our assumption that x is small is
valid
[COCl2] = 0.500 –
[CO] =
[Cl2] =
9
Concept Test:
COCl2 (g) ↔ CO (g) + Cl2 (g) Kc = 8.3 x 10-4 at 360oC
Calculate the equilibrium concentrations of each species at equilibrium
in a 10.0 L flask if:
b.) 0.100 moles of COCl2 decompose
Step 1: Make sure equation is balanced
Step 2: Make an ICE table
Step 3: Calculate concentrations
Step 4: Fill in the ICE table with values
Step 5: Set-up equilibrium expression
COCl2 (g)
↔
CO (g)
+
Cl2 (g)
I
C
E
Kc =
Kc = 8.3 x 10-4 =
if we assume x is small then x =
x 100 =
%
0.0100
Therefore we cannot make this assumption x is significant: use quadratic formula!
a quadratic expression:
x=
- b  b 2 - 4ac
2a
x=
x=
10
x cannot be negative!! Remember x is the change – you cannot
have a negative change! Product must be formed!
Therefore, the only value for x that makes any sense is
x=
Therefore, the equilibrium concentrations are:
[CO] =
M
[Cl2] =
M
[COCl2] =
M
Concept Test:
PCl3 + Cl2 ↔ PCl5
Which way will the reaction shift if PCl5 is siphoned out of the reaction vessel?
(PCl5 removed)
Which way will the reaction shift if more PCl5 is added to the reaction vessel?
Which way will the reaction shift if Cl2 is removed from the reaction vessel?
If PCl3 is removed from the reaction vessel?
Concept Test:
Given 5.00 moles of gas, which is put in a 1.00 L container
results in a concentration of 5.00 M
if the same moles of gas is placed in a 2.00 L container,
the concentration is?
M
if the same number of moles of gas is placed in a 0.500 L container
the concentration is?
M
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Concept Test:
Given the following reactions predict which direction
they will shift if heat is ADDED to each of them:
CaO(s) + H2O(l)  Ca(OH)2 H = -82 kJ
CaCO3 (s)  CO2 (g) + CaO(s) H = 178 kJ
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