At a constant temperature, how do the surface tensions of diesel fuel and vegetable oil compare to that of water?

The correct answer is that the surface tensions of diesel fuel and vegetable oil are less than that of water. This is because surface tension is a measure of the cohesive forces between liquid molecules; stronger intermolecular forces result in higher surface tension. Water has particularly strong hydrogen bonding, which contributes to its high surface tension compared to many other liquids.

Both diesel fuel and vegetable oil are made up of molecules that do not exhibit hydrogen bonding to the same extent as water. Diesel fuel, being a hydrocarbon, has weaker van der Waals forces, while vegetable oil primarily consists of triglycerides with weaker molecular interactions than those found in water. Consequently, both diesel fuel and vegetable oil manifest lower surface tensions when compared to water, indicating that they spread more easily than water and are less resistant to being disturbed at the surface.

This understanding is crucial in applications such as aerial pesticide application, where the behavior of liquids in the air and on plant surfaces can affect the effectiveness and precision of pesticide delivery.