Resources | Subject Notes | Chemistry
This section covers electrolysis, redox processes, standard electrode potentials, and fuel cells. These topics are fundamental to understanding chemical reactions involving electron transfer.
Electrolysis is the process of using an electric current to drive a non-spontaneous chemical reaction. It involves the decomposition of a compound when electricity is passed through it.
An electrolytic cell consists of a power source (e.g., a battery) connected to an electrochemical cell. The cell contains an electrolyte, which is a substance that conducts electricity when dissolved in a solvent.
At the electrodes, oxidation and reduction reactions occur:
The rate of electrolysis depends on several factors:
Redox reactions involve the transfer of electrons. Oxidation is the loss of electrons (increase in oxidation state), and reduction is the gain of electrons (decrease in oxidation state). A substance that loses electrons is the reducing agent, and a substance that gains electrons is the oxidizing agent.
Oxidation states are a way of assigning a charge to an atom in a chemical compound. They are used to track electron transfer in redox reactions.
Redox reactions are balanced using methods like the half-reaction method.
Standard electrode potential (E°) is a measure of the tendency of a substance to be reduced. It is measured relative to the standard hydrogen electrode (SHE), which has a potential of 0 V.
A table of standard electrode potentials for various metals and ions is essential for predicting the spontaneity of redox reactions.
| Substance | Standard Electrode Potential (V) |
|---|---|
| Hydrogen Ion (aq) | 0.00 |
| Sodium Ion (aq) | -2.71 |
| Copper(II) Ion (aq) | +0.34 |
| Silver Ion (aq) | +0.80 |
| Zinc Ion (aq) | -0.76 |
| Iron(II) Ion (aq) | -0.44 |
The cell potential (Ecell) for a redox reaction can be calculated using the following formula:
$$E_{cell} = E_{cathode} - E_{anode}$$If Ecell is positive, the reaction is spontaneous. If it is negative, the reaction is non-spontaneous.
A fuel cell is an electrochemical device that converts the chemical energy of a fuel (e.g., hydrogen) and an oxidant (e.g., oxygen) directly into electrical energy.
A typical fuel cell consists of an anode, a cathode, and an electrolyte.
At the anode, the fuel is oxidized, releasing electrons. These electrons flow through an external circuit to the cathode, where they are combined with an oxidant to produce electricity. Ions migrate through the electrolyte to maintain charge neutrality.