Key Concepts
- First Law: ΔU = Q - W
- Second Law: ΔS ≥ 0
- Carnot Efficiency: η = 1 - Tc/Th
- Heat Transfer: Q = mcΔT
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Thermodynamics Overview
Thermodynamics is the study of energy, heat, work, and how they interrelate. The four laws of thermodynamics form the foundation of this field.
Key concepts include:
- Conservation of energy (First Law)
- Entropy and irreversibility (Second Law)
- Absolute zero temperature (Third Law)
- Thermal equilibrium (Zeroth Law)
Laws of Thermodynamics
If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
This law defines temperature and thermal equilibrium.
ΔU = Q - W
The change in internal energy of a system equals the heat added to the system minus the work done by the system.
The entropy of an isolated system never decreases.
Heat cannot spontaneously flow from a colder location to a hotter location.
As temperature approaches absolute zero, the entropy of a system approaches a constant minimum.
Absolute zero cannot be reached in a finite number of steps.
Thermodynamic Processes
Constant temperature (ΔT = 0)
For ideal gas: ΔU = 0, Q = W
Example: Slow expansion/compression in thermal contact with reservoir
No heat transfer (Q = 0)
ΔU = -W
Example: Rapid expansion/compression with insulation
Constant pressure (ΔP = 0)
W = PΔV
Example: Heating gas in cylinder with free piston
Constant volume (ΔV = 0)
W = 0, ΔU = Q
Example: Heating gas in rigid container
Key Formulas
ΔU = Q - W
Change in internal energy = Heat added - Work done by system
η = Wout/Qin = 1 - Qout/Qin
Carnot Efficiency: ηCarnot = 1 - Tc/Th
Q = mcΔT (sensible heat)
Q = mL (latent heat)
Conduction: Q/t = kAΔT/d
ΔS = Qrev/T
For irreversible processes: ΔS > Q/T