Question

Consider two electrochemical reaqctions. Reaction A results in the transfer of 2 mol of electrons per mole of reactant and generates a current of 5 A on an electrode 2 cm² in area. Reaction B results in the transfer of 3 mol of electrons per mole of reactant and generates a current of 15 A on an electrode 5 cm² in area. What are the net reaction rates for reactions A and B (in moles of reactant per square centimeter per second)? Which reaction has the higher net reaction rate?

Answer 1

The rate of the electrochemical reaction per unit area is given by

where r is the Reaction Rate (in mol s^-1 cm^-2)

i is the Current Generated (in A)

n is the Number of moles of electrons per mole of reactant

F is Faraday's Constant= 96,500 C mol^-1

A is the Electrode Area (in cm²)

(Unit of current should be expressed in terms of Columb per second, C s^-1 to obtain reaction rate in mol s^-1 cm^-2)

Net Reaction Rate for Reaction A:

Given: Number of moles of A, n=2 moles

Current generated, i=5 A=5 C s^-1

Electrode Area, A= 2cm²

Thus reaction rate is

Net Reaction Rate for Reaction B:

Given: Number of moles of B, n=3 moles

Current generated, i=15 A=15 C s^-1

Electrode Area, A= 5cm²

Thus reaction rate is

Reaction A has higher net reaction rate.