A weak acid and a strong acid of the same concentration
will produce the same amount of product from the same amount of reactant
but the weak acid will take longer to do it.
The ionisation of a strong acid is complete. A weak acid is only partly ionised.
The ionisation of a weak acid is reversible.
ethanoic acid (in water) hydrogen ion + ethanoic ion
CH3CO2H(aq) H+(aq) + CH3CO2-(aq)
The number of hydrogen ions produced by a weak acid is small.
When they have reacted with (for example) magnesium
more of the ethanoic acid molecules ionise to produce
more hydrogen ions and ethanoic ions (see Le Chatelier’s Principle).
Eventually all of the ethanoic acid molecules ionise
to react with the magnesium