Something to think about

The relationship between the value of k, the rate constant, and temperature is given by the Arrhenius equation:

k = A exp(–E_a/RT)

where k is the rate constant, A is another constant sometimes known as the Arrhenius constant but more usually as the frequency factor (or pre-exponential factor), E_a is the activation energy for the reaction, R is the gas constant and T is the temperature in Kelvin.

In theory you should know how to express this in logarithmic format but both the Arrhenius equation and its logarithmic form are provided in the Data booklet so you only really need to know how to use it. It is worth relating this to the Nature of Science (and to TOK) by stressing that this an example of an empirical relationship as it cannot be proven mathematically. Note that in the 'Something to think about' on the page for sub-topic  6.1 Collision theory & rates of reaction  I have used the Arrhenius equation to show that the rule of thumb which says that raising the temperature by ten degrees doubles the rate of reaction depends very much upon the value of the activation energy.

The equation is named after the Swedish chemist, Svante Arrhenius, who is perhaps more famous for being the first person to realise that electrolytes are dissociated into their positive and negative ions in aqueous solution and that the more dilute the solution the greater the degree of dissociation. There is a cautionary tale here – don’t let your teacher just dismiss your ideas out of hand. When Arrhenius submitted his work on the dissociation of electrolytes for his doctoral thesis at the University of Uppsala in 1884 the staff at the university thought his work was substandard and awarded him the lowest possible pass mark. Just 19 years later in 1903, after the brilliance of his revolutionary work on electrolytes had been fully recognized, he was awarded the Nobel Prize in Chemistry.