Final answer:
The molar entropy of a molecule tends to increase with its molecular weight due to the increased ways in which the molecules can vibrate.
Step-by-step explanation:
The association between molar entropy and the molecular weight of a molecule is that greater numbers of atoms in a molecule increase the ways in which the molecules can vibrate, leading to an increase in the number of possible microstates and the system entropy. This means that as the molecular weight of a molecule increases, the molar entropy also tends to increase.