Question

Using the reaction and the *E*∘ given below

2Co3+(aq)+2Cl−(aq)→2Co2+(aq)+Cl2(g) *E*∘*=*0.46
V

what is the cell potential at 25 ∘C if the concentrations are
[Co3+]= 3.10×10^{−2}*M* , [Co2+]= 0.732 *M* ,
and [Cl−]= 0.544 *M* and the pressure of Cl2 is
*P*Cl2= 9.80 atm ?

2)At 57.0 ∘C , what is the maximum value of *Q* needed to
produce a non-negative *E* value for the reaction

SO4^2−(aq)+4H+(aq)+2Br−(aq)⇌Br2(aq)+SO2(g)+2H2O(l)

In other words, what is *Q* when *E*=0 at this
temperature?

Answer #1

To solve this for cell potential, we will use the Nernst equation:

E_{cell}= E^{o}_{cell} - RT/nF lnQ

where E_{cell} represents the cell potential, R= gas
constant= 0.0821 Latm/K/mol, T= temperature, n= number of electrons
involved in the redox reaction, Q= activity coefficient

To know "n", let us break down the redox equation into separate equations at the anode and cathode.

Anode reaction: 2Cl^{-} = Cl_{2} +
2e^{-}

Cathode reaction: (Co^{3+} + e^{-}
=Co^{2+}) multiply this equation by two and add it to anode
equation to arrive at the final equation.

From the above reactions, we see that n=2

Now, the Nernst equation can be rewritten as:

E_{cell}= E^{o}_{cell}- 0.0591/n log Q
(On substituting the value of R=0.0821, T=298.15K, F=96500C, ln=
2.303log)

E_{cell}= 0.46- 0.0591/2 log
[Co^{2+}]^{2} P_{Cl2}/
[Co^{3+}]^{2} [Cl-]^{2}

E_{cell}= 0.46 - 0.0591/2 log 0.732 X 0.732 X 9.8 / .031
X .031 X .544 X .544

= 0.334 V.

1) For the reaction
2Co3+(aq)+2Cl−(aq)→2Co2+(aq)+Cl2(g). E∘=0.483 V what is the cell
potential at 25 ∘C if the concentrations are[Co3+]= 0.685
M , [Co2+]= 0.417 M , and [Cl−]=
7.70×10−2M and the pressure of Cl2 is
PCl2= 6.60 atm ?
2)Part A
At 63.0 ∘C , what is the maximum value of the reaction quotient,
Q , needed to produce a non-negative E value for
the reaction
SO42−(aq)+4H+(aq)+2Br−(aq)⇌Br2(aq)+SO2(g)+2H2O(l)
In other words, what is Q when E=0 at this
temperature?Express your answer...

At 57.0 ∘C , what is the maximum value of Q needed to
produce a non-negative E value for the reaction
SO42−(aq)+4H+(aq)+2Br−(aq)⇌Br2(aq)+SO2(g)+2H2O(l)
In other words, what is Q when E=0 at this
temperature?
Express your answer numerically using two significant
figures.
2)Calculate the
pK=−log(K) at 25∘C for
each of the following reactions (K is equilibrium
constant).
Pb(s)+2H+(aq)→Pb2+(aq)+H2(g)
Cl2(g)+Sn2+(aq)→Sn4+(aq)+2Cl

BACKROUND:
E=E∘−(0.0592/n)logQ
The reaction quotient has the usual form
Q=[products]^x/[reactants]^y
A table of standard reduction potentials gives the voltage at
standard conditions, 1.00 M for all solutions and 1.00 atm
for all gases. The Nernst equation allows for the calculation of
the cell potential E at other conditions of concentration
and pressure.
-------------------------------------
For the reaction
2Co3+(aq)+2Cl−(aq)→2Co2+(aq)+Cl2(g). E∘=0.483
V
what is the cell potential at 25 ∘C if the concentrations are
[Co3+]= 0.592 M , [Co2+]= 0.866 M , and [Cl−]=...

At 70.0 ∘C , what is the maximum value of the reaction quotient,
Q, needed to produce a non-negative E value for
the reaction
SO42−(aq)+4H+(aq)+2Br−(aq)⇌Br2(aq)+SO2(g)+2H2O(l)
In other words, what is Q when E=0 at this
temperature?

At 73.0 ∘C , what is the maximum value of the reaction quotient,
Q, needed to produce a non-negative E value for
the reaction
SO42−(aq)+4H+(aq)+2Br−(aq)⇌Br2(aq)+SO2(g)+2H2O(l)
In other words, what is Q when E=0 at this
temperature? And the sovle for the pH?

Determine the free energy(ΔG) from the standard cell
potential (Ecell0 ) for the
reaction:
2ClO2-(aq)+Cl2(g)→2ClO2(g)+
2Cl-(aq)
where:
ClO2+e-→ClO2-Ered0
=+0.954 V.
Cl2+2e-→2Cl-Ered0
=+1.36 V.
ΔG=+79 kJ
ΔG=-790 kJ
ΔG=-79 kJ
ΔG=-0.79 kJ

Consider the reaction
Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s) at 69 ∘C , where [Fe2+]= 3.00
M and [Mg2+]= 0.210 M .
Part A
What is the value for the reaction quotient, Q, for the
cell?
Part B
What is the value for the temperature, T, in
kelvins?
Part C
What is the value for n?
Part D
Calculate the standard cell potential for
Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s)
Part E
For the reaction
2Co3+(aq)+2Cl−(aq)→2Co2+(aq)+Cl2(g). E∘=0.483
V
what is the cell potential at 25 ∘C if the concentrations are
[Co3+]=...

Given:
Cr3+(aq)+3e– ⇌Cr(s);E°=−0.74 V
Cl2(g)+2e– ⇌2Cl−(aq);E°=1.36
What is the standard Gibbs free-energy change for the following
reaction? (F = 96485 C per mole of electrons).
2Cr(s) +3Cl2(g) ⇔2Cr3+(aq) +6Cl−(aq)
Select one:
a. −1215 kJ
b. −231.3 kJ
c. −983 kJ
d. −322.4 kJ
e. 2309 kJ

± The Nernst Equation and pH
Sulfuric acid is a very strong acid that can act as an oxidizing
agent at high concentrations (very low pH, or even negative pH
values). Under standard conditions, sulfuric acid has a low
reduction potential,
SO42−(aq)+4H+(aq)+2e−⇌SO2(g)+2H2O(l), +0.20
V
which means it cannot oxidize any of the halides F2, Cl2, Br2,
or I2. If the H+ ion concentration is increased, however, the
driving force for the sulfuric acid reduction is also increased
according to Le Châtelier's...

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