Question

(a) Which electrode of a voltaic cell, the cathode or the anode, corresponds to the higher potential energy for the electrons? (b) What are the units for electrical potential? How does this unit relate to energy expressed in joules? (c) What is special about a standard cell potential?

Short answer

(a) In a voltaic cell, the anode has a higher potential energy for electrons compared to the cathode, as it is the source of electrons and they flow towards the cathode. (b) The unit of electrical potential is the volt (V). It is related to energy in joules (J) using the formula \(E = Q * V\), where E is the energy, Q is the charge, and V is the electrical potential. (c) A standard cell potential (\(E^0\)) represents the cell potential under standard conditions (298 K temperature, 1 atm pressure, and 1 M concentration for all aqueous species). It indicates the spontaneous nature of a cell reaction under these conditions.

Step-by-step solution

(a) Cathode or Anode: Higher Potential Energy for Electrons

In a voltaic cell, the anode is the electrode where the oxidation reaction occurs, while the cathode is the electrode where the reduction reaction occurs. Electrons are released at the anode as oxidation takes place and are then transferred to the cathode where reduction takes place. Since the anode is the source of electrons and they flow towards the cathode, the anode has a higher potential energy for electrons compared to the cathode.

(b) Units for Electrical Potential and Relation to Energy in Joules

The unit of electrical potential is the volt (V), named after Alessandro Volta. It measures the potential energy per unit charge and can be defined as the work done to move a unit charge from one point to another in an electric field. The relation between electrical potential and the energy in joules (J) can be shown using the formula: \[E = Q * V\] where E is the energy in joules, Q is the charge in coulombs (C), and V is the electrical potential in volts. Therefore, 1 volt can be defined as the potential difference across which 1 coulomb of charge gains or loses 1 joule of energy.

(c) Standard Cell Potential

A standard cell potential, denoted as \(E^0\), is the cell potential under standard conditions, which means a temperature of 298 K (25℃), a pressure of 1 atm, and a concentration of 1 M for all the aqueous species involved in the half-cell reactions. The standard cell potential can provide valuable information about the spontaneous nature of a cell reaction. If it is positive, the cell reaction will spontaneously occur under standard conditions. On the other hand, if it is negative, the cell reaction will not occur spontaneously under standard conditions.