Thermodynamics Cheatsheet
Basic Concepts
- Thermodynamic System: The region of the universe under study.
- Surroundings: The rest of the universe.
- State Functions: Properties that depend only on the current state of the system, not how it got there. Examples include internal energy (U), enthalpy (H), and entropy (S).
- Path Functions: Properties that depend on the path taken to reach a certain state. Examples include work (W) and heat (Q).
Laws of Thermodynamics
- First Law: Energy cannot be created or destroyed, only transferred or converted from one form to another. Mathematically, this is expressed as
ΔU = Q - W, where ΔU is the change in internal energy of the system, Q is the heat transferred to the system, and W is the work done by the system.
- Second Law: The entropy of the universe tends to increase in any spontaneous process. Mathematically, this is expressed as
ΔS_universe = ΔS_system + ΔS_surroundings > 0, where ΔS_universe is the change in entropy of the universe, ΔS_system is the change in entropy of the system, and ΔS_surroundings is the change in entropy of the surroundings.
- Third Law: It is impossible to reach absolute zero (0 K) in a finite number of steps.
Thermodynamic Processes
- Isothermal: A process that occurs at constant temperature.
- Adiabatic: A process that occurs without any heat exchange with the surroundings.
- Isobaric: A process that occurs at constant pressure.
- Isochoric: A process that occurs at constant volume.
Enthalpy
- Enthalpy: A state function that represents the heat content of a system. Mathematically, this is expressed as
H = U + PV, where H is enthalpy, U is internal energy, P is pressure, and V is volume.
- Enthalpy Change: The change in enthalpy of a system during a process. Mathematically, this is expressed as
ΔH = ΔU + PΔV.
Entropy
- Entropy: A state function that represents the degree of disorder of a system. Mathematically, this is expressed as
ΔS = Q/T, where ΔS is the change in entropy, Q is the heat transferred, and T is the temperature.
- Gibbs Free Energy: A state function that combines enthalpy and entropy to predict the spontaneity of a process. Mathematically, this is expressed as
ΔG = ΔH - TΔS.
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