Andrew It is convenient to separate an overall redox reaction into two half-reactions (see previous page) because the reduction and oxidation processes which make up the overall reaction of an electrochemical cell are separated in space. Reduction occurs in one electrode compartment and oxidation in the other, and the process occurring in a given compartment is described by one or other of … Read more
Oxidation is defined as the removal of electrons from a species, while reduction is the addition of electrons to a species. Any reaction in which there is a transfer of electrons from one species to another is thus called a redox reaction. Any redox reaction may be expressed as the difference of two half-reactions, which by convention are always written as … Read more
An electrochemical cell consists of two electrodes, which are simply metallic conductors, in contact with an ionic conductor called the electrolyte. (Though the most commonly encountered electrolytes are ionic solutions, they may also be liquids, e.g. molten potassium bromide, or solids, e.g. solid silver iodide. The only criterion is that the substance must be an ionic conductor.) A single … Read more
When the ionic strength of a solution is too high for the Debye-Hückel limiting law to be valid (ie the molality of the solution is too high), the mean activity coefficient may be estimated from the extended Debye-Hückel law: where B is a dimensionless constant, most simply regarded as a fudge factor This expression allows reasonable estimation of the mean activity coefficient … Read more
Coulombic interactions between ions in solution are relatively strong, long-range forces compared to the other types of intermolecular force in solution. They are thus an important contributor to the non-ideality of ionic solutions, and in the Debye-Hückel theory of such solutions, they are taken to dominate the non-ideality to such an extent that all other contributions … Read more
An ideal solution may be defined as one in which the interactions between all the species present are equal (equivalent to saying ΔH of mixing is zero). Ionic solutions are strongly non-ideal, primarily due to the strong, long-range Coulombic interactions between ions. To compensate for the non-ideality, we introduce the activity of the solute as an effective concentration in all thermodynamic calculations. The … Read more
There are three main ‘reactive species’ in organic chemistry; 1. The Nucleophile: In general, a reactive species with an available pair of electrons. In practice, this splits neatly into two categories – neutral species with a lone pair (e.g. H2O where the Oxygen has two lone pairs) and species with a negative charge (anionic) (e.g. OH–, the hydroxide ion). 2. The Electrophile: … Read more
We have established that in order for a reaction to occur at all, ΔG < 0, however, we still have not concluded anything about the rate of reaction. This is the realm of kinetics. For example, petrol at room temperature is stable, although volatile. Cars do not spontaneously explode; the petrol sits in the tank essentially … Read more
Now we have discussed, and looked at, various factors affecting the reactivity of a species, and which types of reagents attack where, we can look at the variation of these factors from one structure to another, and hope these factors also affect the course, and rate, of a reaction. Firstly, a basic tenet of chemistry is that … Read more
Probably one of the most useful tools for discussing conformation (a subject we have touched on) is the Newman Projection. This is representation of a view looking along the bond of a molecule of interest. For example, the following diagram is a Newman Projection of the staggered form of ethane: The circle represents the nearest carbon atom, and … Read more