12. Standard electrode potential is defined under specific standard conditions: $1 \text{ M}$ concentration for ions, $1 \text{ atm}$ pressure for gases, and $25^\circ C$ temperature. Therefore, pressure, concentration of ions, and temperature are factors that define or affect whether a potential is "standard". The overall energy change of a full cell is a consequence of the cell potential, not a factor that determines the standard electrode potential of a half-cell. The final answer is $\boxed{\text{B overall energy change}}$. 13. The conventional representation for a half-cell typically places the solid electrode first, followed by the aqueous ion. For a copper system, this means the copper metal ($\text{Cu}_{(s)}$) is in contact with its ions ($\text{Cu}^{2+}_{(aq)}$). The single vertical line $|$ represents the phase boundary between the electrode and the electrolyte. The final answer is $\boxed{\text{A Cu}_{(s)} | \text{Cu}^{2+}_{(aq)}}$. 14. A device consisting of two half-cells that converts chemical energy into electrical energy through spontaneous redox reactions is called an electrochemical cell (specifically, a galvanic or voltaic cell). The final answer is $\boxed{\text{B electrochemical cell}}$.