Are acid-base reactions always double displacement?

In order for the reactions to take for a double displacement, there needs to be two reactants, which in turn will yield two products.

The basic reaction for a double replacement react takes the following format:

##AB+CD→CB+AD##

In the case of the the acid-base reaction, the reactants are an acid and a base.

Let's look at an example

Aqueous hydrochloric acid reacts with sodium hydroxide which will yield aqueous sodium chloride and water

##HCl(aq) + NaOH(aq) --> NaCl(aq) + H_2O (l) ##

In a reaction between an acid and a base the typical outcome is a salt formed by the positive ion from the base and the negative ion from the acid.

In this case the positive potassium ion ##(Na^+)## and the negative chorine ion from hydrochloric acid ##(Cl^-)## to form the salt ## NaCl##

The positive hydrogen ##(H^+)## from the acid and the negative hydroxide ion ##(OH^−)## from the base form the water ## HOH ##or ## H_2O##

So to answer your question, Yes, acid-base reactions will always be double displacement, but they are commonly known as a special double displacement reaction called, Neutralization reaction