The Equivalence of Current Density at an Interface and Reaction Rate

The Equivalence of Current Density at an Interface and Reaction Rate 

It has been mentioned that in heterogeneous kinetics (the province of chemistry) the typical reaction would be the catalytic combination of hydrogen and oxygen to form water on a platinum surface, and the way of measuring the rate would be to follow the change in pressure arising from the reaction, and to convert this by means of a simple phenomenological equation to a reaction rate in moles per unit area and time. 

It is easy to relate this current density to the many familiar expression for the rate in terms of moles/cm s. Let the current density be given by the symbol i (current per unit area and time, e.g., A/m /s ) then the number of coulombs which are passing in the time t is given by definition as / t, where i is in A cm and t is in seconds. A constant called the Faraday (which has a value of 96,500 C/mole) is associated with every mole of charge so that if in an electrochemical reaction one passes n electrons in one act of the overall reaction the number of coulombs flowing is nF, or n X 96,500 coulombs per mole every time the reaction occurs once (in the molar sense). 

therefore, we divide the number of coulombs which actually flow in the time t by the number of electrons associated with one act of the overall reaction, we would have the number of times this reaction took place in the time t. If we make this t one second we have 

To exemplify this, let us consider the hydrogen evolution reaction  

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