Thermodynamics Explained
Thermodynamics studies heat, work, and energy. Learn the laws, state variables, and limits on efficiency.
๐ Laws of Thermodynamics
- Zeroth: defines temperature via thermal equilibrium
- First: energy conservation (ฮU = Q โ W)
- Second: entropy increases in isolated systems
- Third: reaching absolute zero is unattainable
๐งช Heat Engines
Carnot efficiency ฮท = 1 โ T_c/T_h sets an upper bound for any heat engine operating between two temperatures.
โ Frequently Asked Questions
1) What is entropy?
A state function measuring disorder and the direction of spontaneous change.
A state function measuring disorder and the direction of spontaneous change.
2) Is perpetual motion possible?
No; the laws forbid devices that create energy or violate entropy.
No; the laws forbid devices that create energy or violate entropy.
3) Micro vs macro?
Statistical mechanics links particle behavior to macroscopic laws.
Statistical mechanics links particle behavior to macroscopic laws.
4) Reversibility?
Idealized processes with no entropy production.
Idealized processes with no entropy production.
5) Real engine losses?
Friction, heat leaks, finite-rate processes.
Friction, heat leaks, finite-rate processes.
6) Heat pumps?
Move heat from cold to hot using work; COP measures performance.
Move heat from cold to hot using work; COP measures performance.
7) Enthalpy vs internal energy?
H = U + pV is convenient for constant-pressure processes.
H = U + pV is convenient for constant-pressure processes.
8) Free energies?
Gibbs/Helmholtz capture useful work under constraints.
Gibbs/Helmholtz capture useful work under constraints.
9) Phase diagrams?
Show states and transitions like boiling and melting.
Show states and transitions like boiling and melting.
10) Absolute entropy?
Set by third law; zero at 0 K for perfect crystals.
Set by third law; zero at 0 K for perfect crystals.