Now, these guys weaken bonds by adding an H plus ion to one of the reactants, thereby lowering the activation energy and speeding up our reaction. For example, let's look at the following reaction. Now, this actually involves a bit of organic chemistry but bear with me and I'll try to explain it. What happens is one of the H molecules, one of the H ions is added to this age group, to this oxygen group and this weakens this bond here. So then the hydroxide form act as a base or a nucleophile attacking this carbon bond, thereby displacing this weaker bond. And it was weakened by the h group, remember?