MCAT® Exam flashcards
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Entropy (ΔS)
Flip cardA 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.
Hund's Rule
Flip cardStates 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.
Chirality
Flip cardThe 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.