im a bit confused on how and why surface tension and viscosity decrease with increasing temperature?
Kinetic energy of the molecules increases with increasing temperature; therefore, the attraction of adjacent molecules for each other is less effective.
Surface tension and viscosity are properties of fluids that can change with temperature. Let's start by explaining each of these properties separately and then understand their relationship with temperature.
1. Surface Tension:
Surface tension is the force acting at the surface of a liquid that tends to minimize its surface area. It is a measure of the cohesive forces between the molecules of a liquid. These forces create a "skin" or "film" on the surface, giving rise to surface tension.
When the temperature increases, the kinetic energy of the molecules also increases. As a result, the average distance between the molecules increases, and the intermolecular forces become weaker. This weaker intermolecular attraction leads to a decreased surface tension. The increase in temperature disrupts the cohesive forces and reduces the resistance of the liquid to flow at the surface.
To measure surface tension, various methods can be used, such as the capillary rise method or the drop weight method. These methods involve quantifying the force required to break the liquid's surface.
2. Viscosity:
Viscosity is a measure of a fluid's resistance to flow. It is related to the internal friction within the fluid. In simpler terms, viscosity determines how easily a fluid can be poured or flow.
With increasing temperature, the kinetic energy of the molecules increases, and they move more rapidly. This increased movement disrupts the organized flow of molecules in the fluid, reducing the internal friction and thereby decreasing the viscosity. The fluid becomes thinner and flows more easily.
Measuring viscosity can be done using different methods and instruments, such as viscometers or rheometers. These instruments measure the time it takes for a fluid to flow through a small opening or the force required to make the liquid flow.
In summary, as the temperature increases, the increased kinetic energy of the molecules weakens the intermolecular forces responsible for surface tension and disrupts the ordered flow of molecules in the fluid, reducing the viscosity. Both phenomena are a consequence of molecular behaviors at higher temperatures.