Thermodynamics Cheat Sheet

Key Definitions

• Thermodynamics: The study of heat, work, and energy transformations. ✅

• System: A specified portion of matter or space under study. ✅

• Surroundings: Everything outside the system. ✅

• Isothermal Process: A process at constant temperature. ✅

• Adiabatic Process: A process with no heat exchange. ✅

Important Concepts

Laws of Thermodynamics

• Zeroth Law: If two systems are in thermal equilibrium with a third, they are in equilibrium with each other. ✅

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

• Second Law: Entropy of an isolated system always increases. ✅

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

Key Formulas

• First Law of Thermodynamics:

• ΔU: Change in internal energy

• Q: Heat added to the system

• W: Work done by the system

• Work Done in Isothermal Process:

• n: Moles of gas

• R: Universal gas constant (8.314 J/(mol·K))

• T: Absolute temperature

• Vi/Vf: Initial and final volume

• Efficiency of Carnot Engine:

• Tc: Absolute temperature of cold reservoir

• Th: Absolute temperature of hot reservoir

Common Mistakes to Avoid

Common Mistake: Confusing heat (Q) with temperature (T); heat is energy transfer, temperature is a measure of thermal energy.

Memory Tricks

Tip: "Q = W + ΔU" — Remember the First Law of Thermodynamics: Heat added equals work done plus change in internal energy.

Key Diagrams

   +-------+          +-------+
   |       |   Q     |       |
   |   A   | <------> |   B   |
   |       |          |       |
   +-------+          +-------+
       |                  |
      W|                  |W
       |                  |
   +-------+          +-------+
   |       |   Q     |       |
   |   C   | <------> |   D   |
   |       |          |       |
   +-------+          +-------+