(i) Thermodynamic principles can be employed to derive a relation between electrical energy and the maximum amount of work (W_max),
(ii) The maximum amount of work obtainable from the cell is the product of charge flowing per mole and maximum potential difference E, through which the charge is transferred.
W_max = -nFE ..... (1)
where, n = number of moles of electrons transferred
F = Faraday (96495 coulombs)
E = emf of the cell
According to thermodynamics,
W_max = ΔG ...(2)
From (1) and (2)
ΔG = - nFE
when E is positive, ΔG is positive ΔG will be negative and the cell reaction is spontaneous.

(i) When it is placed on the right-hand side of the zinc electrode, the hydrogen electrode reaction is,
2H⁺+ 2e^- ➝ H²
The electrons flow to the SHE and it acts as the cathode.
(ii) When the SHE is placed on the left hand side, the electrode reaction is
H₂ ➝ 2H⁺+ 2e^- 
The electrons flow to the copper electrode and the hydrogen electrode acts as the anode.

Overall redox reaction
Zn_(s) + Cu²⁺_aq ⟶ Zn²⁺_aq + Cu_(s)
oxidation half reaction:
Zn_(s)+ Cu²⁺_aq ⟶ Zn²⁺_aq + 2e^-
reduction half reaction:
Cu²⁺ + 2e^- ⟶ Cu_(s)

(i) The emf of the standard hydrogen electrode is Zero volts.
Fe / Fe³⁺ Fe²⁺, H²_(atm)pt E = 0.771 V
E_measured = E_R- E_L
(ii) emf of SHE = 0
E_measured = 0.771V - 0 = 0.771V.
(iii) ∴ The other half cell connected is Standard Hydrogen Electrode (SHE).