Surface Tension

Definition

Surface tension is the property of a liquid that causes its surface to behave like a stretched elastic membrane. This phenomenon occurs due to the cohesive forces between liquid molecules, which are stronger at the surface where molecules are in contact with air or another medium. Surface tension is critical in various physical behaviors of fluids, such as droplet formation and capillary action, influencing how fluids interact with solids and gases.

5 Must Know Facts For Your Next Test

1. Surface tension is typically measured in dynes per centimeter (dyn/cm) or millinewtons per meter (mN/m), with water having a surface tension of about 72.8 dyn/cm at room temperature.
2. Temperature affects surface tension; as temperature increases, surface tension generally decreases due to increased molecular motion disrupting cohesive forces.
3. Surfactants are substances that lower surface tension when added to a liquid, which can enhance wetting properties and affect how liquids spread on surfaces.
4. The phenomenon of insects walking on water is attributed to surface tension, which allows them to remain atop the liquid without sinking.
5. Surface tension plays a key role in processes like inkjet printing, where controlling fluid behavior on surfaces is essential for creating precise patterns.

Review Questions

• How does cohesion contribute to the concept of surface tension in liquids?
  • Cohesion is the force of attraction between similar molecules, which is particularly strong among liquid molecules at the surface. This strong attraction pulls surface molecules inward, creating an effect that makes the liquid's surface behave like an elastic membrane. The greater the cohesion among the molecules, the higher the surface tension will be, affecting various physical behaviors of fluids.
• Discuss how temperature changes can impact the surface tension of a liquid and provide an example.
  • Temperature changes have a direct effect on surface tension because as temperature increases, the kinetic energy of the molecules also increases. This heightened molecular motion weakens the cohesive forces at the surface, leading to a decrease in surface tension. For example, when water is heated, its surface tension drops, allowing it to spread more easily over surfaces and affecting processes like boiling or washing.
• Evaluate the significance of surfactants in modifying surface tension and their practical applications.
  • Surfactants are compounds that significantly lower surface tension when added to liquids. They disrupt cohesive forces among liquid molecules, allowing for better wetting and spreading properties. This modification is crucial in various applications such as detergents, which enhance cleaning by allowing water to penetrate more effectively into fabrics and surfaces. Additionally, surfactants are used in pharmaceuticals and food products to stabilize emulsions and foams.

Related terms

Cohesion: The attraction between similar molecules, which contributes to the formation of surface tension in liquids.

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

Meniscus: The curved surface of a liquid in a container, formed due to surface tension and the interaction between the liquid and the container's walls.