Surface Tension

Definition

Surface tension is a physical property of liquids that describes the elastic-like force existing at the surface of a liquid, which causes it to behave as if it were covered by a stretched elastic membrane. This phenomenon arises due to cohesive forces between liquid molecules, which are stronger at the surface where the molecules experience an imbalance of intermolecular forces compared to those in the bulk of the liquid. Surface tension is crucial in various applications, from capillary action to the behavior of droplets and bubbles.

5 Must Know Facts For Your Next Test

1. Surface tension is measured in force per unit length, typically expressed in units like Newtons per meter (N/m).
2. Temperature has a significant effect on surface tension; as temperature increases, surface tension usually decreases due to reduced cohesive forces between molecules.
3. Detergents and surfactants can lower surface tension, which is why they help in cleaning by allowing water to spread and penetrate more effectively.
4. Surface tension is responsible for phenomena such as water striders being able to walk on water and the formation of spherical droplets.
5. The value of surface tension varies between different liquids; for example, water has a higher surface tension than most organic solvents due to strong hydrogen bonding.

Review Questions

• How does cohesion contribute to the phenomenon of surface tension in liquids?
  • Cohesion refers to the attractive forces between similar molecules, and it plays a vital role in creating surface tension. At the surface of a liquid, molecules experience stronger cohesive forces with each other than with the air above them. This imbalance leads to a 'skin' effect on the liquid's surface, making it behave as if it were under tension. Understanding this helps explain behaviors such as droplet formation and the ability of some insects to walk on water.
• Discuss how temperature variations can impact surface tension and provide examples of real-world applications affected by this change.
  • Temperature has a direct influence on surface tension; as temperatures rise, surface tension typically decreases due to weakened cohesive forces among liquid molecules. For example, in industrial processes such as inkjet printing or spray coating, controlling temperature can optimize the spreading of liquids on surfaces. Additionally, this concept applies to natural systems where varying temperatures affect water bodies and their interactions with organisms that rely on surface tension for locomotion or feeding.
• Evaluate how surfactants affect surface tension and analyze their significance in both everyday life and industrial applications.
  • Surfactants are substances that reduce surface tension by disrupting cohesive forces among liquid molecules. In everyday life, this property is crucial for cleaning agents like detergents that allow water to penetrate dirt and stains more effectively. In industrial applications, surfactants are used in formulations like paints and emulsions, enhancing stability and performance. By evaluating their roles across different fields, it becomes clear that understanding surfactants’ effects on surface tension not only aids in improving product efficacy but also promotes sustainable practices by optimizing resource use.

Related terms

Cohesion: The intermolecular attraction between like molecules, which is responsible for the formation of droplets and the structure of liquids.

Adhesion: The attraction between unlike molecules, which plays a significant role in capillary action and wetting phenomena.

Capillary Action: The ability of a liquid to flow in narrow spaces without external forces, which is driven by the interplay of surface tension, cohesion, and adhesion.