THERMODYNAMICS Cheat Sheet

Key Definitions

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

• System: Part of the universe under study.

• Surroundings: Everything outside the system.

• Isolated System: No exchange of energy or matter. ✅

• Closed System: Energy exchange possible, but not matter. ✅

• Open System: Both energy and matter can be exchanged. ✅

Important Concepts

Laws of Thermodynamics

• Zeroth Law: If A is in thermal equilibrium with B, and B with C, then A is with C. ✅

• First Law: Energy cannot be created or destroyed, only transformed. ΔU = Q - W ✅

• Second Law: Heat cannot spontaneously flow from cold to hot. ✅

• Third Law: As temperature approaches absolute zero, entropy approaches a constant minimum. ✅

Processes

• Isothermal: Constant temperature. ✅

• Adiabatic: No heat exchange. ✅

• Isochoric: Constant volume. ✅

• Isobaric: Constant pressure. ✅

Key Formulas

• First Law: ΔU = Q - W

• ΔU: Change in internal energy

• Q: Heat added to the system

• W: Work done by the system

• Work (W): W = PΔV (for gas expansion) ✅

• Efficiency (η): η = (W_out / Q_in) × 100% ✅

• Entropy change (ΔS): ΔS = Q_rev / T ✅

Common Mistakes to Avoid

Common Mistake: Confusing heat (Q) with temperature (T). Heat is energy, temperature is a measure of kinetic energy.

Memory Tricks

Tip: "QWERTY" —

• Q: Heat added

• W: Work done

• E: Energy conservation

• R: Reversible processes

• T: Temperature constancy

• Y: Yield of work

Key Diagrams

  +-----------------+
  |                 |
  |      System     |
  |                 |
  +-----------------+
          | 
          |  Heat/Q
          | 
  +-----------------+
  |                 |
  |   Surroundings  |
  |                 |
  +-----------------+