Strong acids fully dissociate in water, whereas weak acids only partially dissociate.

To elaborate, when an acid is introduced to water, it donates a proton (H$^+$) to a water molecule, resulting in the formation of a hydronium ion (H$_3$O$^+$). This process is referred to as dissociation. The degree to which an acid dissociates in water is what determines its classification as either a strong or weak acid.

Strong acids, such as hydrochloric acid (HCl), nitric acid (HNO$_3$), and sulfuric acid (H$_2$SO$_4$), completely dissociate in aqueous solutions. This means that each molecule of a strong acid donates its proton to a water molecule, leading to a high concentration of hydronium ions in the solution and consequently a low pH value.

In contrast, weak acids, such as acetic acid (CH$_3$COOH) and carbonic acid (H$_2$CO$_3$), only partially dissociate in water. Not all molecules of a weak acid will donate their protons, resulting in a lower concentration of hydronium ions and a higher pH value compared to strong acids.

The degree of dissociation for weak acids can be affected by the concentration of the acid and the temperature of the solution. Increasing either the concentration or the temperature may enable more of the weak acid to dissociate.

It is also crucial to understand that the labels ‘strong’ and ‘weak’ refer specifically to an acid’s ability to donate protons, rather than its corrosiveness or potential danger. A weak acid can be just as corrosive or hazardous as a strong acid, depending on various factors, including its concentration.