MCAT® Exam flashcards

A thermodynamic property that is a measure of the disorder or randomness of a system. An increase in disorder corresponds to a positive change in entropy (ΔS > 0), while a decrease in disorder corresponds to a negative change (ΔS < 0).

• Gases have higher entropy than liquids, which have higher entropy than solids.
• Systems tend towards higher entropy (Second Law of Thermodynamics).
• Entropy increases with increasing temperature and volume.

Memory trick: Entropy's Easy: More Mess, More Entropy. Less Mess, Less Entropy.

States that every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin.

• Maximizes the number of unpaired electrons.
• Applies to degenerate orbitals (orbitals of the same energy).
• Used in conjunction with the Aufbau principle and Pauli exclusion principle.

Memory trick: Hund's Rule: Half-fill first, then pair up.

The property of a molecule that is non-superimposable on its mirror image, often due to the presence of a chiral center (e.g., a carbon atom bonded to four different groups).

• Molecules are 'handed' like human hands.
• Often (but not always) involves a chiral carbon (sp3 hybridized carbon with four different substituents).
• Lack of a plane of symmetry is a key indicator.

Memory trick: Chiral Can't Copy, it's not Superimposable.