Question

Standard Entropies Methane, CH S 186.3J mol- K- Ethane, C2H S 229.6J mol- K-1 Propane, C3Hg 270.3J mol- K-1 S Why do larger more complex molecules have larger entropies?
brief answer and explanation please

Answer 1

Entropy is the measure of randomness or disorderness of a molecule. The standard entropy of molecules increases with the in increase in the size and the complexities of the molecules because as the size and the complexities of the molecules increase the randomness of the molecules increases. The ability of the molecule to exist in different forms and different orders increases. A more complex molecules has more ability to change the arrangement of its atoms, bonds, groups, bondlengths etc. contributing more to its entropy.

For example: Methane can arrange its 4 hydrogen atoms only in four different ways by exchanging their positions while in ethane this can be done in 6 different ways as there are 6 hydrogen atoms. Also, ethane can change its orientation through the bonds between the two carbon atoms. These factors again increases in propane. Therefore, the standard entropy increases from methane to ethane and the to propane.