According to the concept of entropy, what will likely happen to most molecules over time?

I love your question. It reminds me of the great short story by that title. In Pynchon's fiction, just as all closed systems lose energy over time until a 'heat-death' occurs wherein motion ceases, so too does culture have a tendency to lose differentiation and slide toward what Callisto, his character and mouthpiece, terms 'the Condition of the More Probable.'
But scientifically speaking, " Entropy change has often been defined as a change to a more disordered state at a molecular level. In recent years, entropy has been interpreted in terms of the dispersal of energy," says one authority. In other words, molecules over time tend to break down.