Entropy (S)
A property related to the degree of disorder in a system. Highly ordered systems have low entropies.
The change in entropy (∆S) in the course of a reaction is the difference between the entropies of the
products and the reactants.
Equilibrium
The state of balance in which the forward and reverse reaction rates are equal. In a system at
equilibrium, the concentrations of all species will remain constant over time unless there is a
change in the reaction conditions. See Le Châtelier’s principle.
Equilibrium constant
The ratio of the concentration of the products to the concentration of the reactants for a certain
reaction at equilibrium, all raised to their stoichiometric coefficients.
Equivalence point
The point in a titration at which the number of equivalents of the species being added to the
solution is equal to the number of equivalents of the species being titrated.
Esters
Compounds of the general formula R-COO-R’.
Ethers
Compounds of the general formula R-O-R’.
Excess reagent
In a chemical reaction, any reagent whose amount does not limit the amount of product that can be
formed. Compare to Limiting reagent.
Excited state