Isomers are molecules that have the same chemical formula but different arrangements of atoms, as shown here for two isomers of pentane, C₅H₁₂.
(b) Which isomer do you expect to have the higher standard molar entropy? Explain.

Key Concepts

Isomerism

Isomerism refers to the phenomenon where two or more compounds have the same molecular formula but differ in the arrangement of atoms. This can lead to distinct physical and chemical properties, as seen in structural isomers like the different forms of pentane. Understanding isomerism is crucial for predicting how these compounds will behave in various chemical contexts.

Standard Molar Entropy

Standard molar entropy is a measure of the amount of disorder or randomness in a system at standard conditions (1 bar and 25°C). It is an important thermodynamic property that reflects the number of accessible microstates for a given substance. Generally, more complex molecules with greater degrees of freedom and larger surface areas have higher entropies.

Effect of Molecular Structure on Entropy

The molecular structure significantly influences the entropy of isomers. For instance, branched isomers tend to have lower entropy than their straight-chain counterparts due to reduced molecular motion and fewer conformations. In the case of pentane isomers, the straight-chain form typically exhibits higher entropy because it has more possible arrangements and interactions compared to its branched isomer.