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thermodynamics · how energy flows

The rules of change, seen through heat and energy

From temperature and pressure to entropy and cycles, see the paths heat and work travel.

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01A State Is a Set of Properties

Fix the scope with a system and boundary, and see a state as a bundle of properties, one point on the P-V plane

#balloon#thermos#pressure cooker

02Pressure and Temperature Measure Molecular Motion

Collisions make pressure, average molecular speed makes temperature; thermal equilibrium, kelvin, and the zeroth law

#tire pressure#thermometer#weather pressure

03Pressure and Temperature Decide a Substance's Phase

The P-T phase diagram splits solid, liquid, gas; plus the P-v saturation dome, triple and critical points

#melting ice#boiling water#dry ice

04Boundary Work Is the Area Under the P-V Curve

Expansion is work; W = ∫P dV is the area under the curve, with path dependence and sign convention

#engine piston#syringe#bicycle pump

05Energy Is Conserved: dU = Q - W

Internal energy changes by heat in minus work out; U is a state property, with adiabatic, isochoric, and cycles

#hand warmer#insulation#thermos

06Enthalpy H = U + PV Is Natural at Constant Pressure

H = U + PV. Heat at constant pressure is ΔH, flow work is PV; why H is natural for flow and constant pressure

#boiler#heater#steam pipe

07Ideal Gas PV = nRT, and Each Process Traces Differently

PV=nRT ties P, V, T together. Isothermal is a hyperbola, isobaric and isochoric are lines, adiabatic a steeper PV^γ curve

#balloon#scuba tank#AC refrigerant

08Heat Engine: A Cycle That Turns Heat into Work

Take Q_H, deliver work W, dump Q_C. A cycle gives Q_H = W + Q_C, efficiency η = W/Q_H = 1 - Q_C/Q_H

#car engine#jet engine#power plant

09The Second Law: Heat Has a Direction

Heat flows hot to cold on its own. Kelvin-Planck (η<1) and Clausius (a fridge needs W) are one law; real processes are irreversible

#cooling coffee#refrigerator#melting ice

10The Carnot Cycle: The Most Efficient Engine

Two isotherms + two adiabats. η = 1 - T_C/T_H is the ceiling, set by the temperature ratio alone; underneath, Q_H/T_H = Q_C/T_C

#car engine#refrigerator#power plant

11Entropy: A Measure of Spreading and the Arrow of Time

A state function dS = dQ_rev/T. The universe obeys ΔS_total ≥ 0 (arrow of time), equality only when reversible; statistically S = k ln Ω

#ink spreading#melting ice#broken cup

12The Rankine Cycle: The Steam Power Plant

Four parts: boiler, turbine, condenser, pump. The phase change trades heat near constant T with tiny pump work. η = W_net/Q_H

#power plant#nuclear plant#steam turbine

13The Otto and Diesel Cycles: Gasoline and Diesel Engines

Gas cycles, no phase change. Otto burns at constant V, Diesel at constant P. η = 1 − 1/r^(γ−1); diesel wins with a higher r

#gasoline car#diesel car#truck engine

14Refrigeration: Running a Cycle Backward to Pump Heat Uphill

An engine reversed: work W moves heat from cold to hot. Q_H = Q_C + W, rated by COP = Q_C/W, Carnot COP = T_C/(T_H−T_C)

#refrigerator#air conditioner#heat pump

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