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HS Chemistry - Intermolecular Forces

Properties of Liquids

Overview of The Page

This page will cover:

  • What properties of liquids are based on intermolecular forces?

There are several properties of liquids that are based on intermolecular forces:

  • Viscosity is how readily something flows. Something that flows less readily has greater viscosity. For example, honey flows less readily than water, which means it has greater viscosity. Stronger intermolecular forces increase viscosity.

  • Capillary Action:

    • Cohesion is how strongly molecules remain attracted to themselves. An example of cohesion is a drop of water remaining attracted to itself rather than spreading over the tabletop. Stronger intermolecular forces increase cohesion.

    • Adhesion is how strongly molecules remain attracted to another substance. An example of adhesion is how, in a beaker, water tends to cling to the sides, forming a meniscus. Stronger intermolecular forces increase adhesion.

  • Surface tension is the property of a liquid that allows it to resist an external force due to its cohesion. Stronger intermolecular forces increase surface tension.

  • Vapor pressure is the amount of pressure exerted by gases on a liquid in a closed system. The higher the vapor pressure is, the more frequently the gas particles will collide with the liquid particles. They’ll transfer some of their kinetic energy to the liquids, gradually leading over time to some of the liquid gaining enough energy to become gases. A more volatile liquid will take a shorter amount of time to do this. Stronger intermolecular forces will cause the liquid molecules to remain connected to other liquid molecules for longer before turning into gas. Thus, stronger intermolecular forces increase the amount of time this takes and decrease the volatility of the liquid.

  • Miscibility is how easily two liquids mix together. Polar liquid molecules have high miscibility with other polar liquid molecules, as permanent dipole forces dipole-dipole bonds are able to form between the molecules. Nonpolar liquid molecules have high miscibility with other nonpolar liquid molecules, as induced dipole forces dispersion forces are able to form. However, polar liquid molecules do not have high miscibility with other polar liquid molecules, as neither induced dipole nor permanent dipole forces are able to form between them.