What is electrochemistry? What are redox reactions? Explain the difference between a galvanic and an electrolytic cell.

Electrochemistry is the branch of chemistry that deals with the relationship between electrical energy and chemical reactions, particularly the interconversion between them. In other words, it studies how chemical reactions can produce electricity and how electricity can drive chemical reactions. A key concept in electrochemistry is redox reactions. Redox (short for reduction-oxidation) reactions involve the transfer of electrons between chemical species. In a redox reaction, one species loses electrons, undergoing oxidation, while the other species gains electrons, undergoing reduction. Balancing redox reactions requires understanding the changes in oxidation states of the participating chemical species.

A galvanic cell, also known as a voltaic cell, is a type of electrochemical cell that converts chemical energy into electrical energy through spontaneous redox reactions. In a galvanic cell, the oxidation half-reaction and the reduction half-reaction occur in separate compartments connected through a salt bridge or a porous membrane. These compartments are called the anode and the cathode. The anode is where oxidation occurs, while the cathode is where reduction occurs. Electrons flow from the anode to the cathode through an external circuit, which can be used to power various electrical devices. In the meantime, ions in the electrolyte migrate between the compartments in a way that maintains electrical neutrality. An example of a galvanic cell is the Daniel cell, which uses the following redox reaction: \[ Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s) \] In this cell, Zinc is oxidized and loses two electrons, while Copper ions receive the electrons and are reduced to metallic copper. The flow of electrons from Zinc to Copper creates an electrical current.

An electrolytic cell is another type of electrochemical cell, but unlike the galvanic cell, it uses electrical energy to drive a non-spontaneous redox reaction. In other words, an external voltage is applied to force the redox reaction to occur in the direction that would not happen spontaneously. In an electrolytic cell, the anode and cathode are still used for oxidation and reduction processes, but the difference is that the anode is now the positive electrode, and the cathode is the negative electrode. The external voltage provided should be greater than the cell potential of the redox reaction to drive it. One common application of electrolytic cells is the electrolysis of water, where electrical energy is used to split water molecules into hydrogen and oxygen gases: \[ 2H_2O(l) \rightarrow 2H_2(g) + O_2(g) \] In this case, the electrolysis occurs at two different electrodes, with oxygen gas forming at the anode and hydrogen gas forming at the cathode. In conclusion, electrochemistry deals with the relationship between electrical and chemical energies, with redox reactions being the center of attention. A galvanic cell generates electrical energy from spontaneous redox reactions, whereas an electrolytic cell uses electrical energy to drive non-spontaneous redox reactions.