Why does oil spread on a pan?

1. Cohesive and Adhesive Forces: Oil molecules have a stronger cohesive force (attraction to each other) compared to their adhesive force (attraction to the pan's surface). As a result, the oil tends to minimize contact with the pan and prefers to spread out to increase the surface area of the oil layer.

2. Surface Tension: The surface tension of oil is lower than the surface tension of water. Surface tension is the energy required to increase the surface area of a liquid. The lower surface tension of oil allows it to spread more easily across the pan's surface.

3. Density: The density of oil is lower than the density of water. This difference in density causes the oil to float on top of the water. In a pan, the heavier water droplets remain below the oil layer, allowing the oil to spread more freely on the surface.

4. Viscosity: Viscosity refers to the resistance of a fluid to flow. Oil generally has a lower viscosity compared to water and other liquids. The low viscosity of oil means it can flow more easily and spread out on the pan's surface.

5. Molecular Interactions: The molecular structure of oil plays a role in its spreading behavior. Oil molecules, particularly unsaturated fats, have a "kinked" shape that prevents close packing. This kinked structure reduces the cohesive forces between oil molecules and contributes to its ability to spread.

The combination of these factors causes oil to spread on a pan, forming a thin film that coats the surface. The properties of different types of oils can influence the extent to which they spread and behave on a heated surface.