In a double displacement reaction: 

A double displacement reaction, also known as a metathesis reaction, is a type of chemical reaction where the ions of two reactants are exchanged to form two new compounds. These reactions typically occur in aqueous solutions, resulting in the formation of a precipitate, gas, or a neutral molecule like water.

In a double displacement reaction, the cations and anions of the reacting compounds swap places. This process can involve ionic compounds, and sometimes covalent compounds are also formed as products. The general formula for a double displacement reaction can be represented as:

AB + CD → AD + CB

For example, consider the reaction between sulfuric acid (H₂SO₄) and lithium hydroxide (LiOH):

H2SO4 + 2LiOH → Li2SO4 + 2H2O

In this reaction, the sulfate ion (SO₄^2-) from sulfuric acid is replaced by the hydroxide ion (OH^-) from lithium hydroxide, leading to the formation of lithium sulfate (Li₂SO₄) and water (H₂O). This exchange of ions to form new products is the hallmark of a double displacement reaction.

Such reactions often lead to the formation of a precipitate, which is an insoluble solid that separates from the solution. In other cases, a gas may be released or a neutral molecule like water may form, depending on the nature of the reactants involved.

Key Features of Double Displacement Reactions:

• Involves the exchange of ions between two reactants.
• Forms new compounds as products.
• Often results in the formation of a precipitate, gas, or water.

Hence, a double displacement reaction plays a significant role in various chemical processes, especially in fields like analytical chemistry and industrial manufacturing.