๐น Thermodynamic system: A finite part of the universe under observation.
Boundaries can be real/imaginary. Types: open (mass & energy transfer), closed (only energy), isolated (no transfer).
๐น Surroundings: Everything outside the system. System + surroundings = universe.
๐น State function: Property that depends only on current state, not path taken. Examples: Pressure (P), Volume (V), Temperature (T), Internal energy (U), Enthalpy (H), Entropy (S).
Work (W) & heat (Q) are NOT state functions; they are path functions.
Internal energy U: state function; ฮU = Q + W (first law). Q & W individually path dependent but ฮU independent.
๐ง State functions (PVT UHS): โPublic Very Tasty U-Haul Serviceโ โ P (pressure), V (volume), T (temp), U (int. energy), H (enthalpy), S (entropy).
๐ง Not state functions: โQWERTYโ โ Q (heat) & W (work) are path functions (like typing path on keyboard).
๐ง Open/closed/isolated: โOCEANโ โ Open: Coffee cup (mass & heat) ; Closed: sealed flask (only energy) ; Isolated: thermos (ideally nothing).
๐ TIP: State functions are exact differentials (dU, dH) while work/heat are inexact (ฤQ, ฤW).
๐ MDCAT TRICK: In MCQ, if you see โdepends on pathโ โ work/heat; if โinitial & final onlyโ โ state function.
GUIDELINES: Draw boundary around system in every problem. Identify transfer. For state fn: just look at start/end, ignore how you got there. Practice 10 MCQs below.
Master thermodynamics in 4 days: