JEE Thermodynamics Revision Cheat Sheet

Key Definitions

• Thermodynamics: Study of heat, work, and energy transformations.

• System: The part of the universe under study (open, closed, isolated).

• Surroundings: Everything outside the system.

• State Function: Property depending only on the state (e.g., internal energy).

• Path Function: Property depending on the path taken (e.g., work, heat).

Important Concepts

Laws of Thermodynamics

• Zeroth Law: If A = B and B = C, then A = C (thermal equilibrium).

• First Law: ΔU = Q - W (energy conservation).

• Second Law: Entropy of an isolated system never decreases.

• Third Law: Entropy approaches a constant minimum as temperature approaches absolute zero.

Processes

• Isothermal: Constant temperature (Q = W).

• Adiabatic: No heat exchange (Q = 0).

• Isochoric: Constant volume (W = 0).

• Isobaric: Constant pressure (W = PΔV).

Key Formulas

• ΔU: Change in internal energy

• Q: Heat added to the system

• W: Work done by the system

W = PΔV ✅

• P: Pressure

• ΔV: Change in volume

S = k * ln(W) ✅

• S: Entropy

• k: Boltzmann's constant

• W: Number of microstates

Common Mistakes to Avoid

Common Mistake: Confusing heat (energy transfer) with temperature (measure of energy).

Common Mistake: Forgetting that work done on the system is negative (W < 0).

Memory Tricks

Tip: "Q = W + ΔU" — Remember that heat added equals work done plus change in internal energy.

Key Diagrams

      Isothermal Process
         +---------+
         |         |
         |         |
         |         |
         +---------+

      PV Diagram
      Pressure
        |
        |       Isotherm
        |      /
        |     /
        |    / 
        |   /
        |  / 
        +----------------
                Volume