Chem 209
DUE 3/10/08
1.
KEY
Quiz 6 TAKEHOME
Write the Kc and Kp expression for the reactions below.
2Cl2(g) + 2H2O(g)  4 HCl(g) + O2(g)
4 CuO(s) + CCl4(g)  CO2(g) + 4 Cu(s) + 2 Cl2O(g)
SO3(g)  SO2(g) + ½ O2(g)
Kc 
HCl4 O2 
Cl2 2 H2O2
Kp 
Kc 
CO2 Cl2O2
CCl4 
Kp 
SO2 O2 2
Kc 
SO3 
4
PHCl
PO2
PCl2 2 PH22O
PCO2 PCl2 2O
PCCl4
1
1
P4(s) + 10 Cl2(g)  4 PCl5(s)
1
Kc 
Kp 
Cl2 
2
K c  Cl2 
CCl4(l)  C(s) + 2 Cl2(g)
Kp 
10
PSO2 PO22
PSO3
1
PCl102
K p  PCl2 2
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2. For which of the following reactions does Kp = Kc There may be more than one?
NH3(g) + 3O2(g)  2N2(g) + 6H2O(l)
3 H2(g) + N2(g)  2NH3(g)
CO(g) + Cl2(g)  COCl(g) +Cl(g)
H2(g) + I2(g)  2 HI(g)
2 SO2(g) + O2(g)  2 SO3(g)
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3 Consider the following equilibrium?
NH4CO2NH2(s)  2 NH3(g) + CO2(g)
Kp = 2.5 10 at 310 K
What are the equilibrium pressures of NH3 and CO2 at 310 K?
NH4CO2NH2(s)
initial
change
equil
2
K p  PNH
P
3 CO2

2 NH3(g)
+
0
2x
2x
3
 2x  x   4x 3  2.5  104
 2.5  104 
  3.97  102
x  3 
4


PCO2  x  3.97  102 atm
PNH3  2x  7.94  102 atm
1
CO2(g)
0
x
x
Chem 209
DUE 3/10/08
KEY
Quiz 6 TAKEHOME
___________________________________________________
4.
Consider the exothermic reaction 4 NO2(g) + O2(g)  2 N2O5(g).
Indicate the effect of the following stresses on the equilibrium.
(shift to products, shift to reactants, no effect)
a) a decrease in the pressure of NO2 (shifts to reactants)
b) an increase in the pressure of N2O5 (shifts to reactants)
c) a decrease in temperature. (shift to products)
d) addition of a catalyst (no effect)
e) an increase in the volume of the container holding the gases. (shifts to reactants)
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5.
Consider the reaction 4 CuO(s) + CCl4(g) 
Kp at 400
2(g) + 4 Cu(s) + 2 Cl2O(g).
°C is 625 for this reaction. Write the algebraic equation needed to solve for the equilibrium
pressures of CCl4(g), CO2(g), and Cl2O(g) at 400 °C. Assume initially that the concentrations
are 1.0 atm for CCl4(g) , 2.0 atm for CO2(g) and 3.0 atm for Cl2O(g).
4 CuO(s)
4 Cu(s)
+
2 Cl2O(g)
+ CCl4(g)  CO2(g) +
initial
change
equil
-
1.0
x
1.0 - x
Kp 
PCl2 2OPCO2
PCCl4
2.0
x
2.0 - x
-
3.0
2x
3.0 - 2x
2

3.0  2x  2.0  x 

 625
1.0  x 
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6.
For the reaction 2 SO2(g) + O2(g)  2 SO3(g), Kc = 0.200 at 100 °C.
If 1.0 moles of SO2 is mixed with 0.50 moles of SO3 and 0.50 moles of O2 in a 5.0 L
chamber, will there be more or less than 1.0 mole of SO2 when equilibrium is reached. (Hint:
use the reaction quotient to determine the answer)
SO3   0.50 mol  0.10 M
5L
SO2   1.0 mol  0.20 M
O2   0.50 mol  0.10 M
5L
Q
5L
SO3 2  0.12  2.5
SO2 2 O2  0.22 0.1
since Q > K there are too many products and thus will be more SO2(s) at equilibrium
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7. Find the concentration of Mg2+ ions in a saturated solution of MgF2 (Ksp = 6.6x10-9)
MgF2(s)
i
c
e

Pb2+
0
x
x
+
2F
0
2x
2x

 
K sp  Mg2 F
1
2
 x(2x)2  4x 3
1
 K  3  6.6  10 9  3
  1.2  10 3
x   sp   
4
 4 


2+

[Mg ] = x = 1.210 
2
Chem 209
DUE 3/10/08
KEY
Quiz 6 TAKEHOME
__________________________________________________________________________
8. Assume a reaction has a H of 55.0 kJ/mol. It's equilibrium constant at 25 oC is 6.410-2.
Find the equilibrium constant at 35 oC.
K
H  1
1 


ln 35  

K 25
R  T35 T25 
 55000Jmol 1  1
K 35
1 

 


1
1 
K 25
 8.314JK mol  308K 298K 
K
ln 35  6615K  3.247  10 3 K 1  3.356  10 3 K 1
K 25
ln

ln
ln
e


K 35
 6615K   1.090  10  4 K 1  0.72
K 25
K 35
K 25
 e 0.72
K 35
 2.056
K 25


K 35  k 25 2.056  6.4x10 2  0.132
3
