1.2.1: Affinity for Spontaneous Chemical Reaction
A given closed system is prepared using ethyl ethanoate(aq) in an alkaline solution. The composition of the system changes spontaneously as a consequence of chemical reaction. The latter is described by the following chemical equation.
\[\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq}) \rightarrow \mathrm{CH}_{3} \mathrm{COO}^{-}(\mathrm{aq})+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\mathrm{aq}) \nonumber \]
At each stage, the extent of chemical reaction is represented by the symbol \(\xi\). The composition of the system varies with time as the reaction proceeds. At any given instant we characterise the rate of chemical reaction by \(\mathrm{d} \xi / \mathrm{dt}\). We also ask ‘why did chemical reaction proceed in this direction?’ The answer is − the chemical reaction is driven in that direction by the affinity for spontaneous change, symbol \(\mathrm{A}\) [1-3]. The affinity \(\mathrm{A}\) for spontaneous chemical reaction is defined by the second law of thermodynamics which states that,
\[\mathrm{T} \, \mathrm{dS}=\mathrm{q}+\mathrm{A} \, \mathrm{d} \xi \nonumber \]
\[\text { where } A \, d \xi \geq 0 \nonumber \]