Surface Tension

Definition

Surface tension is the elastic-like force existing at the surface of a liquid that causes it to behave as if its surface were covered with a stretched elastic membrane. This phenomenon occurs due to the cohesive forces between liquid molecules, leading to a minimized surface area, and plays a significant role in various interfacial phenomena, influencing processes such as wetting, capillarity, and the formation of droplets.

5 Must Know Facts For Your Next Test

1. Surface tension is measured in units of force per unit length (e.g., dynes/cm or N/m), indicating the amount of energy required to increase the surface area of a liquid.
2. Factors such as temperature, impurities, and surfactants can affect surface tension by altering the cohesive forces between molecules.
3. In biological systems, surface tension is crucial for processes like the formation of alveoli in the lungs, where surfactants reduce surface tension to prevent collapse.
4. Surface tension is responsible for phenomena like water beads on a waxed car surface or insects walking on water without sinking.
5. The concept of surface tension has practical applications in various industries, including paint formulation, inkjet printing, and pharmaceuticals.

Review Questions

• How does cohesion contribute to the phenomenon of surface tension in liquids?
  • Cohesion plays a vital role in creating surface tension by causing liquid molecules to attract each other. This mutual attraction leads to a minimization of the liquid's surface area, forming an 'elastic' layer at the surface. The stronger the cohesive forces between molecules, the higher the surface tension, which explains why some liquids can support objects that are denser than themselves.
• Discuss how temperature and impurities can influence the surface tension of a liquid and provide examples.
  • Temperature directly affects surface tension; as temperature increases, kinetic energy rises, leading to greater molecular movement and a decrease in cohesive forces, which reduces surface tension. Impurities can also alter surface tension; for instance, adding soap to water decreases its surface tension by disrupting the cohesive interactions among water molecules. These changes can significantly impact processes like wetting and spreading in various applications.
• Evaluate the importance of surface tension in real-world applications and biological systems, citing specific examples.
  • Surface tension is essential in both real-world applications and biological systems. For example, in industrial applications like inkjet printing, controlling surface tension ensures even spreading of ink on surfaces. In biology, surfactants produced in the lungs reduce surface tension within alveoli, preventing their collapse during exhalation. Understanding these implications helps improve product formulations and enhances physiological functions crucial for life.

Related terms

Cohesion: The attractive force between molecules of the same substance, which contributes to the phenomenon of surface tension.

Capillarity:

The ability of a liquid to flow in narrow spaces without external forces, often influenced by surface tension.

Interfacial Tension:

The tension existing at the interface between two immiscible liquids or between a liquid and a gas.