Which of the following reactions will have the larger emf under standard conditi

Question

Which of the following reactions will have the larger emf under standard conditions? Why? Calculate Delta G for the reaction Example 17.3 Voltages listed in textbooks and handbooks are given as standard cell potentials (voltages). What is meant by a standard cell? Were the cells constructed in this experiment standard cells? Why or why not? As a standard voltaic cell runs, it "discharges" and the cell potential decreases with time. Explain. Using standard potentials given in the appendices, calculate the standard cell potentials and the equilibrium constants for the followings: Cu (s) + 2A g^+ (aq) Cu^2 + (aq) + 2 Ag (s) Zn(s) + Fe^2 (aq) Zn^2 + (aq) + Fe(s)

Explanation / Answer

A standard cell is a cell which operates under standard conditions. By standard conditions we mean a temperature of 273 K and a pressure of 1 atm. All the ion species in solutions are at a conc of 1 M, and gases if any are at a pressure of 1 atm.

As the cell runs, the reaction in the cell proceeds in the forward reaction and the reaction quotient Q proceeds towards the equilibrium value Kc.

When Q becomes Kc, the cell is said to have discharged.

In the eqn:

dG = dG0 + RT lnQ, where dG0 = -RT ln Kc

So, dG becomes 0 at eqb.

For the reaction:

Cu(s) + 2Ag+ ----> Cu2+ + 2Ag(s)

Ecell = Eoxid + Ered

Here Cu is getting oxidized and Ag is getting reduced.

Looking from the standard potential table, and putting values we get:

Ecell = -0.159+0.799 = +0.64 V

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