Cohesion

Definition

Cohesion is the intermolecular attraction between like molecules, which contributes to the structural integrity of substances. This property is crucial in phenomena such as surface tension, where cohesive forces between liquid molecules at the surface create a barrier, and in capillary effects, where cohesion helps drive the movement of liquids in narrow spaces. Understanding cohesion helps explain how fluids interact with surfaces and other materials.

5 Must Know Facts For Your Next Test

1. Cohesion is responsible for the high surface tension of water, allowing small insects to walk on its surface.
2. In capillary action, cohesion helps pull water molecules together, while adhesion allows them to cling to the walls of narrow tubes or pores.
3. The stronger the cohesive forces in a liquid, the higher its surface tension will be, affecting various applications in colloid science.
4. Cohesion plays a critical role in maintaining the shape of droplets and bubbles, as they minimize surface area to reduce energy.
5. In biological systems, cohesion is essential for processes like water transport in plants, where it aids in the movement of water from roots to leaves.

Review Questions

• How does cohesion contribute to surface tension in liquids, and why is this important in colloidal systems?
  • Cohesion contributes to surface tension by creating an inward force at the surface of a liquid, as molecules are attracted to each other more strongly than to the air above. This results in a 'skin' on the liquid's surface that resists external forces. In colloidal systems, surface tension influences the stability and behavior of colloidal particles, impacting their interactions and aggregation.
• Discuss how cohesion and adhesion work together in capillary action and its relevance to colloidal systems.
  • Cohesion works alongside adhesion in capillary action, where cohesive forces keep liquid molecules together while adhesive forces allow them to interact with solid surfaces. In colloidal systems, this interaction is crucial for understanding how particles move through porous materials or narrow channels, affecting everything from filtration processes to drug delivery mechanisms.
• Evaluate the role of cohesion in biological systems and its implications for understanding fluid dynamics within living organisms.
  • Cohesion plays a significant role in biological systems by enabling processes like water transport in plants through xylem vessels. This occurs as water molecules stick together due to cohesion, allowing them to rise against gravity during transpiration. Understanding this interaction provides insights into fluid dynamics within living organisms and highlights how molecular forces can impact vital biological functions.

Related terms

Adhesion:

The attraction between unlike molecules, which is important for how liquids interact with surfaces.

Surface Tension: The elastic tendency of a fluid surface that makes it acquire the least surface area possible, primarily due to cohesive forces.

Capillarity:

The ability of a liquid to flow in narrow spaces without the assistance of external forces, influenced by both cohesion and adhesion.