Are Liquids Compressible?

The compressibility of a liquid depends upon its intermolecular bond and the spacing between the molecules. In liquid, this spacing is very low. Aside, repulsive forces exist between the molecules. It is a challenging task to bring the liquid molecules closer, and hence liquids resist compression. Suppose a liquid is kept in a container and a piston is placed at the top. If immense pressure is applied to the piston, the liquid will compress slightly, as shown in the image below. Therefore, only under extraordinary circumstances are liquids slightly compressible.

Example of Incompressibility of Water

Imagine squeezing a water balloon. Water takes whatever shape the balloon takes. Suppose the inside pressure is high. Since water does not compress easily, the balloon will not take the pressure any longer.  It will burst, and water will come out.

As a result of compression, the molecules are confined to a smaller space. Hence, the density increases. The viscosity, which is the ability of a liquid to resist its motion, also increases. The reason is that when molecules are brought closer, the spacing between them becomes so small that the attractive forces start to dominate. The molecules cannot slip on top of each other as freely as they would at atmospheric pressure (normal conditions).

• Liquids can flow freely and take the shape of the container
• Liquids are incompressible under normal circumstances
• Liquid can slightly deform under extremely high pressure