The first row, labelled I, lists the initial conditions: the concentration of acid is "C"0, initially undissociated, so the concentrations of A− and H+ would be zero; "y" is the initial concentration of "added" strong acid, such as hydrochloric acid. If strong alkali, such as sodium hydroxide, is added, then "y" will have a negative sign because alkali removes hydrogen ions from the solution. The second row, labelled C for "change", specifies the changes that occur when the acid dissociates. The acid concentration decreases by an amount −"x", and the concentrations of A− and H+ both increase by an amount +"x". This follows from the equilibrium expression. The third row, labelled E for "equilibrium", adds together the first two rows and shows the concentrations at equilibrium.