attraction force 問題 10 分

Attractive force is a "force", whereas p.e. (potential energy) is an "energy".
Due to the presence of attractive force between molecules, a molecules will experience a potential energy (PE) with respect to the other. This is similar to the fact that an object on earth surface will experience a graviational PE because of the attraction of the earth.
Molecular attractive force (sometimes called van der Waal force) decreases rapidly with increase of distance. The larger the separation between two molecules, the higher the PE is (just compare the case of an object raised to a higher height from earth surface, its PE increases).
When an object solidifies, the moelcules become more close to one another, the strong molecular force thus can [catch] the randomly moving mlecules together and hence their PE decreases because of less separation. The release of potential energy is observed as the latent heat of fusion