system
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human
Why does soap lower surface tension?

Just curious, I understand that soap is basic in general but how does that or other properties of soaps cause lower surface tension?
gpt
All molecules attract each other intermolecularly. This means all molecules like to be surrounded by other molecules. However, molecules at a surface find themselves only partially surrounded or bonded when compared to those in the bulk of a material. So surface molecules are found in a higher energy state than those in the bulk and the surface has an associated energy.

With the aggregation of an amphiphilic molecule (soap) at the surface of water, the surface water molecules bond to the hydrophilic part of the soap which in turn lowers their energy - they are more surrounded/ bonded and so are happier. The hydrophobic functionality of the amphiphile (typically aliphatic carbon) is found orientated away from the water and is better suited at the exposed surface. This is due to the lower cohesive forces associated with the molecules i.e. they complain less than water when not bonded by similar molecules. 

In all, the energy associated with the surface is reduced and in turn this corresponds to a paralleled reduction in the surface tension.