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Both molecules have van der Waals forces of attraction acting between them. However, the stearic acid molecules (C17H35COOH) also have hydrogen bonds between them. These are sometimes referred to as simply "weak bonds", but are better called "intermolecular forces of attractions" - forces of attraction between small discrete molecules.

The higher the temperature - the higher the KE of these molecules - and the faster they move around. It makes sense that as the molecules move slower (at lower temperatures) these forces of attraction are more successful at forming actual bonds between them. 

The attractions don't change - but the bonds do. In the gaseous state there are no bonds. In the liquid state bonds constantly form and break (allowing the molecules to slide past one another). In the solid state the bonds between the molecules are permanent.

Hey Johnny,

When a substance is melted, its molecules gain energy (due to the increase in heat) and due to this energy the molecules move faster (increased velocity). This is why solid paraffin wax becomes liquid - the molecules have more kinetic energy and are thus moving around more. When cooled, the molecules lose energy and move slower - the wax becomes solid. 

This is a very brief answer to your question but its an overview of the kinetic theory of particles. Please message me if you want a detailed explanation and we can talk it through!

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