Determine the overall cell reaction and e cell (at 25 degrees celsius) of a zn electrode in a 1.0 m zn(no3)2 solution and a pb electrode in a 1.0 m pb(no3)2 solution. e (zn2+/zn) = -0.76 v, e (pb2+/pb) = -0.13 v.

what reaction occurs in the cell?

a.) zn(s) + 2h+(aq) > zn2+(aq) + h2 (g)

b.) pb2+(aq) + zn2+(aq) > pb(s) + zn (s)

c.) zn2+(aq) + pb(s) > zn(s) + pb2+(aq)

d.) pb2+(aq) + zn(s) > pb(s) + zn2+(aq)

The right answer is option D and this is because it is a galvanic reaction between two dissimilar metals (Redox half-cell reactions).

Explanation:

To arrive at the answer, you will need to determine the cell reaction, before you calculate the overall Ecell potential.

In order for the cell to be galvanic, the overall cell potential must be a positive value and it must have redox half-cell reactions.

The oxidation/reduction half-cell reactions occur as follows.

Zn  →  Zn2+  +  2e-                                 E0 = -(-0.76) V  (We reversed this because it is an oxidation reaction (as Zn oxidised with ease when compared to Pb), and the other is

Pb2+  +  2 e-  →  Pb                                E0 = -0.13 V  (Reduction reaction)

The overall cell reaction is:

Then, the E cell (standard potential) = 0.76 V + -0.13 V = 0.63 V

However, using the the Nernst equation:, we can calculate now the overall Ecell @ 25 degree Celsius. It states:

Overall Ecell (@25 degree Celsius) = Ecell (standard) - (RT/nF) x lnQ

where

R is the gas constant (8.3145 J/mol·K)

T = 25 degree C = 273K+25 =298K

n = number of moles of electrons transferred = 2

F = Faraday's constant = 96500 C/mol )

Q = reaction quotient, where

Q = [X]x·[Y]y / [A]a·[B]b

where A, B, X, and Y are chemical species; and a, b, x, and y are the reaction coefficients as follows.

a A + b B → x X + y Y

RT/nF = (8.3145 J/mol·K)(298 K)/(2)(96500 C/mol)

RT/nF = 0.0128 J/C = 0.0128 V

Now, we can find the reaction quotient, Q as follows.

We were given each solution concentrations;

Zn(NO3)2 solution = 1.0 M and Pb(NO3)2 solution as 1.0 M

Q = [products]/[reactants] , Q = [Zn2+]/[Pb2+]

Q = 1.0 M / 1.0 M

Q = 1.0

Putting this values into the Nernst Equation to calculate the overall E cell at 25 degree Celsius,

Ecell (@25 degree C) = 0.63 V - 0.0128 V x ln(1.0)

Ecell (@25 degree C) = 0.63 V - 0.0128 V x 0

Ecell (@25 degree C) = 0.63 V - 0

Hence, the right answer to the question is option D (highlighted above) and the Ecell  (at 25 degrees Celsius) is 0.63V

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