Surface tension

Definition

Surface tension is a physical property of liquids that describes the elastic-like force at the surface of a liquid that makes it behave as if it were covered by a stretched elastic membrane. This phenomenon occurs due to cohesive forces between liquid molecules, which causes the surface to minimize its area and resist external force. Understanding surface tension is essential for explaining various processes involving interfaces, such as capillary action, droplet formation, and the behavior of surfactants.

5 Must Know Facts For Your Next Test

1. Surface tension is measured in units of force per unit length, typically in dynes per centimeter (dyn/cm) or Newtons per meter (N/m).
2. The value of surface tension varies among liquids; for example, water has a higher surface tension than many organic solvents due to strong hydrogen bonding.
3. Surface tension decreases with an increase in temperature as the kinetic energy of the molecules increases, leading to weaker cohesive forces.
4. The presence of surfactants significantly lowers the surface tension of a liquid, which can enhance processes like wetting and spreading.
5. Surface tension is responsible for phenomena like water droplets forming spherical shapes and insects like water striders walking on water without sinking.

Review Questions

• How do cohesion and adhesion contribute to the behavior of liquids at their surfaces?
  • Cohesion contributes to surface tension by keeping liquid molecules tightly packed together, creating an elastic-like surface that resists external forces. Adhesion plays a crucial role in how liquids interact with other surfaces, allowing them to spread or climb along surfaces through capillary action. Together, these forces explain why some objects can float on water and how liquids can rise in narrow tubes despite gravity.
• What is the impact of temperature on surface tension and why does it occur?
  • Temperature has a significant effect on surface tension; as temperature increases, surface tension generally decreases. This happens because higher temperatures provide molecules with greater kinetic energy, allowing them to overcome intermolecular forces more easily. As a result, cohesive forces become weaker, leading to a reduction in surface tension. This understanding is important when considering liquid behavior under different thermal conditions.
• Evaluate the role of surfactants in altering surface tension and their practical applications in various fields.
  • Surfactants play a vital role in reducing surface tension by disrupting cohesive forces among liquid molecules. This property makes them essential in many applications, such as detergents that help clean surfaces by allowing water to spread and penetrate better. Surfactants are also used in pharmaceuticals for drug delivery systems and in food science for stabilizing emulsions. Understanding how surfactants affect surface tension allows for innovation across industries by enhancing product effectiveness and efficiency.

Related terms

Cohesion: Cohesion refers to the intermolecular forces that hold similar molecules together, contributing to the surface tension of liquids.

Adhesion: Adhesion is the attractive force between different substances, which plays a role in how liquids interact with surfaces and can influence capillary action.

Surfactant: Surfactants are substances that reduce the surface tension of liquids, allowing them to spread more easily and stabilize emulsions.