Define Advancement and charge - Cell Diagrams?

The electron number or charge number, z, of the cell reaction is defined as the amount of electrons entering at the right terminal per unit advancement of the cell reaction z is a

Figure: Zinc-copper galvanic cell with porous barrier (heavy dashed line) separating two electrolyte solutions. The dashed rectangle indicates the system boundary. (a) Open circuit with isolated system in equilibrium state. (b) Closed circuit.

positive dimensionless quantity equal to |v_e| where v_e is the stoichiometric number of the electrons in either of the electrode reactions whose sum is the cell reaction.

Because both electrode reactions are written with the same value of jej, the advance- ments of these reactions and of the cell reaction are all described by the same advancement variable ξ. For an in?nitesimal change dξ, an amount of electrons equal to z dξ enters the system at the right terminal, an equal amount of electrons leaves at the left terminal, and there is no buildup of charge in any of the internal phases. The Faraday constant F is a physical constant de?ned as the charge per amount of protons, and is equal to the product of the elementary charge (the charge of a proton) and the Avogadro constant: F D eN_A. Its value to five significant figures is F = 96.485 Cmol^-1. The charge per amount of electrons is -F. Thus, the charge entering the right terminal during advancement d ξ is