Reactivity 3.2 — HL Flashcards
What is the standard hydrogen electrode (SHE) and what is its standard electrode potential (E°)?
The SHE consists of a platinum electrode in a solution of 1M H+ ions, with hydrogen gas at 1 atm. It is the reference electrode for measuring standard electrode potentials. Its standard electrode potential (E°) is arbitrarily set to 0 V.
How are standard electrode potentials determined using the SHE?
Standard electrode potentials are determined by connecting a metal electrode to the SHE and measuring the voltage. The SHE acts as either an anode or cathode based on the metal’s reducing power, allowing for the measurement of the metal’s standard electrode potential relative to hydrogen.
What does a positive or negative standard electrode potential indicate?
A positive standard electrode potential indicates a tendency to be reduced (act as an oxidizing agent), while a negative E° suggests a greater likelihood of being oxidized (acting as a reducing agent).
How is the standard cell potential (E°cell) of a reaction calculated?
E°cell = E°(cathode) - E°(anode). This calculation involves subtracting the standard electrode potential of the anode from that of the cathode.
What does a positive E°cell indicate about the spontaneity of a reaction?
A positive E°cell indicates that a reaction is spontaneous in the forward direction under standard conditions.
How is the change in Gibbs free energy (ΔG°) related to the standard cell potential?
ΔG° = -nFE°cell, where n is the number of moles of electrons transferred, F is the Faraday constant (96,485 C/mol), and E°cell is the standard cell potential in volts. A negative ΔG° indicates a spontaneous reaction.
Calculate E°cell and ΔG° for a cell consisting of zinc and copper half-reactions.
E°cell = E°(Cu²⁺/Cu) - E°(Zn²⁺/Zn) = +0.34V - (-0.76V) = +1.10V. ΔG° = -nFE°cell = -2(96,485 C/mol)(1.10 V) = -212 kJ/mol, indicating the reaction is spontaneous.
What is the procedure for experimenting with voltaic cells to determine standard electrode potentials?
Use a simulator to construct voltaic cells with various metal electrodes, measure voltages, and record half-reactions. Compare experimental values with theoretical standard cell potentials.
