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Name
SECTION
TOTAL:
TA Name
Chemistry 130 (1,2)
Dr. J. F. C. Turner
Examination 2
2 hours
Please answer all parts of all questions and show all your work
You may use:
Non-programmable calculators
You may not use:
Any written materials (cards or notes etc) or any other electronic device
1.(a) Write down the chemical equilibrium for the autoprotolysis of water, paying careful attention to the states and
charges, and the value for the equilibrium constant K W .
KW =
(b)
pOH
6 points
Write down the expression for the equilibrium constant K W and the relationship between p K W , pH and
p KW =
6 points
(c)
For an acid and the related conjugate base, write down the relationship between K A , the acid constant, K B ,
the base constant for the conjugate base and K W .
2 points
(d)
Hydrogen selenite, HSeO
3
is a weak acid with an acid constant of K A,HSeO 3 aq 3aq aq
= 4.8 ×10
−9
. In aqueous
2
3aq
H 3O
SeO
solution, it reacts according to the equilibrium HSeO
. Calculate pH and pOH for a
1
0.5 mol L aqueous solution of hydrogen selenite. You may assume that 0.5 x ~0.5 .
(e)
8 points
Write down the acid-base equilibrium that is present in an aqueous solution of sodium selenite, Na 2 SeO3aq .
4 points
−9
(f)
Given that K A,HSeO = 4.8×10 , calculate the pH for a 1.3 mol L1 solution of Na 2 SeO 3aq . You may
assume that 1.3 x ~ 1.3 .
3 aq
8 points
34 points
2.(a) Calcium iodate, Ca IO 32 s , has a solubility constant of 6.47× 106 and is therefore sparingly soluble. Write
down the equilibrium that is present when Ca IO 3 2 s dissolves in water to form a saturated solution.
4 points
(b)
2
aq Calculate the concentration of calcium ion, Ca
, and iodate ion,
IO
3 aq , in the saturated solution in part (a).
6 points
131
3aq
IO
(c)
If radioactive iodate,
is added to the solution in such a way that the solubility constant is exceeded,
will the radioactivity be detected in the solid calcium iodate that is in equilibrium with the solution? Explain your
answer.
4 points
(d)
Write down the relationship between the standard change in Gibbs function, G° , and a general equilibrium
constant K eq
4 points
(e)
Calculate the standard Gibbs function of solution, G
and T = 298 K .
°
sol
, for CaIO 3 2 s , given that R = 8.314 J mol K1
6 points
(f)
1
The standard Gibbs function of formation for IO
and the
3 aq is given by G f IO 3aq = 132.69 kJ mol
2
standard Gibbs function of formation for Caaq
is given by G f Ca aq = 532.60 kJ mol . Calculate an estimate
for the Gibbs function of formation for CaIO 3 2 s using these data and the change in the standard Gibbs function of
solution for Ca IO 32 s .
2
1
8 points
(g)
Calcium iodate can also form the hexahydrate, Ca IO 326 H2 O s , the solubility constant for which is given by
K sp Ca IO 3 26 H2 O s = 7.10× ⋅ 107 . Calculate the change in the standard Gibbs function when Ca IO 326 H2 O s
forms a saturated solution at room temperature, given that R = 8.314 J mol K1 .
6 points
(h)
Assuming that identical solutions are formed in parts (e) and (g), calculate the an estimate for the change in
standard Gibbs function, G r , for the reaction CaIO 3 2 6 H 2 O s Ca IO3 26 H 2 Os together with the
equilibrium constant, given that R = 8.314 J mol K1 and T = 298 K .
8 points
46 points
3.(a)
Write down the relationship between K C and K P for an equilibrium between gaseous reactants and products.
4 points
(b)
Nitrogen trioxide, N 2 O 3 g , is in equilibrium with nitric oxide, NO g and nitrogen dioxide, NO 2g according
to the equilibrium
N 2 O 3 g NO g NO2 g
K P = 4.1
Write down the expression for K P .
4 points
Calculate the value of K C at 298 K for this equilibrium. You may assume that R = 8.314 J mol 1 K 1
(c)
KC =
6 points
(d)
A sample of nitrogen trioxide, N 2 O3 g , is introduced into a vessel, so that the initial pressure of the gas is 0.75
atm. Given that K P = 4.1 , calculate the pressure of NO g , NO 2g and N 2 O3 g when the system has attained
equilibrium at 298 K. The approximation 0.75x ~ 0.75 does not apply in this situation.
P NO =
P NO =
8 points
2
PN
(e)
2
O3
=
Calculate the total pressure in the vessel at equilibrium.
P total =
4 points
(f)
Calculate the the mole fraction of each gas at equilibrium.
x NO
g x NO
2g
xN
2
=
=
O3g 6 points
=
(g)
Write down the equation that gives the temperature dependence of the rate constant.
4 points
(h)
The enthalpy of reaction, H r for N 2 O 3 g NO g NO2 g is H r = 37.9 kJ mol
equilibrium constant at 498 K. You may assume that R = 8.314 J mol 1 K 1
K 498 =
(i)
1
.
Calculate the
6 points
Write down a definition of Le Chatelier's principle
4 points
(j)
Is the value of the equilibrium constant at 498 K for the reaction N2 O3 g NO g NO2 g consistent with Le
Chatelier's principle? Explain your answer.
4 points
50 points
4(a)
Write down the rate law and the integrated rate law for a 2nd order reaction with one reactant, A.
Rate Law
Integrated Rate Law
8 points
(b)
Write down the equation that relates the half-life, t 1/2 of a reaction to the rate constant, k , for a 2nd order
reaction.
4 points
(c)
Mercuric ion, Hg
2+
aq
24aq reacts with oxalate ion, C 2 O
according to the following equation:
22+
2 Hg2+
aq C 2 O4 aq CO 2g Hg 2 aq
Four experiments were performed to determine the rate equation for this reaction, which are given in the table below.
22+
2 Hg2+
aq C 2 O4aq CO2 g Hg 2 aq
Experiment
1
2
3
4
2+
[Hgaq]0 / mol l
0.105
0.105
0.052
0.052
1
2-
[C 2 O4aq ]0 / mol l
0.15
0.30
0.30
0.15
1
5
1
0 / 10 mol l
1.8
7.1
3.5
0.89
min
1
From these data, determine
2+
(i) the order of reaction with respect to [Hg aq]
(ii) the order of reaction with respect to [C2 O24 -aq ]
(iii) the overall order of the reaction.
2+
Order with respect to [ Hg aq
]=
] =
Order with respect to [C2 O42 aq
Overall order for the reaction =
(d)
8 points
Write down the rate law for this reaction.
4 points
(e)
Calculate the rate constant for this reaction paying careful attention to the units of k .
6 points
(f)
What relationship, if any, do the stoichiometric coefficients for this reaction have with the order of the reaction
with respect to each reactant? Justify your answer with as full an explanation as possible.
4 points
The Maxwell-Boltzmann distribution of energies in a perfect gas is given below.
Number of particles
(g)
No reaction
Reaction
Energy / x 104 J mol-1
G
For a certain reaction, only particles above a certain energy, labeled as G, on the diagram are known to react.
Name this energy.
2 points
(h)
Write down the Arrhenius equation for the rate constant k .
4 points
(i)
Read the numerical value for G from the graph and calculate the rate constant for this reaction at 298 K. You
should assume that the pre-exponential factor, A is 1 and that R = 8.314 J mol 1 K 1 .
6 points
n
m
(k)
For a general rate law = k[A ] [B ] , what determines the magnitude of n and m , assuming that this
reaction is elementary in nature?
4 points
50 points