Thermodynamics & Statistical Physics — 55 Terms Defined

Isochoric Process Thermodynamics & Statistical Physics J A thermodynamic process occurring at constant volume, during which no mechanical boundary work is performed. ΔV = 0 ⇒ W = 0, Q = ΔU = n Cv ΔT

Isothermal Process Thermodynamics & Statistical Physics J A thermodynamic change in state occurring at a constant temperature throughout the system. ΔT = 0 ⇒ ΔU = 0, Q = W = n R T ln(V2/V1)

Joule-Thomson Effect Thermodynamics & Statistical Physics K/Pa The temperature change experienced by a real gas when throttled through an insulated porous plug or valve at constant enthalpy. μ_JT = (∂T / ∂P)_H

Latent Heat of Fusion Thermodynamics & Statistical Physics J/kg The amount of thermal energy required to change a unit mass of a substance from solid to liquid at constant melting temperature. Q = m L_f

Latent Heat of Vaporization Thermodynamics & Statistical Physics J/kg The thermal energy required to convert a unit mass of liquid into gas at constant boiling temperature. Q = m L_v

Linear Thermal Expansion Thermodynamics & Statistical Physics K⁻¹ (°C⁻¹) The fractional change in length of a solid material per degree change in temperature. ΔL = α L0 ΔT

Macrostate Thermodynamics & Statistical Physics N/A The macroscopic state of a thermodynamic system defined by observable thermodynamic variables like pressure, volume, temperature, and total energy. Defined by (P, V, T, N, U)

Maxwell Relations Thermodynamics & Statistical Physics Various A set of thermodynamic equations derived from equality of second partial derivatives of thermodynamic potentials (U, H, F, G). (∂T/∂V)_S = -(∂P/∂S)_V, (∂T/∂P)_S = (∂V/∂S)_P, etc.

Maxwell-Boltzmann Distribution Thermodynamics & Statistical Physics s/m The probability distribution describing particle speeds in an ideal gas in thermal equilibrium. f(v) = 4π (m / (2π kB T))^(3/2) v² exp(-m v² / (2 kB T))

Mean Free Path Thermodynamics & Statistical Physics m The average distance traveled by a moving gas particle between successive collisions with other particles. λ = 1 / (√2 π d² n_V)

Microstate Thermodynamics & Statistical Physics N/A A specific detailed microscopic configuration of a thermodynamic system, specifying exact positions and momenta of all constituent particles. S = kB ln Ω

Molar Heat Capacity Thermodynamics & Statistical Physics J/(mol·K) The heat energy required to raise the temperature of one mole of a substance by one Kelvin. C_m = Q / (n ΔT), C_p - C_v = R

Most Probable Speed Thermodynamics & Statistical Physics m/s The particle speed corresponding to the maximum peak of the Maxwell-Boltzmann speed distribution curve. v_mp = √(2 kB T / m) = √(2 R T / M)

Partition Function Thermodynamics & Statistical Physics Dimensionless The central mathematical function in statistical mechanics that encodes statistical properties of a system in thermodynamic equilibrium. Z = ∑ exp(-E_i / (kB T)) = ∑ g_i exp(-E_i / (kB T))

Principle of Mixtures Thermodynamics & Statistical Physics J The heat conservation principle stating that in an isolated system, heat lost by hotter components equals heat gained by cooler components until equilibrium is reached. ∑ Q = 0 ⇒ ∑ m_i c_i (T_f - T_i) = 0

Refrigerator / Heat Pump Thermodynamics & Statistical Physics Dimensionless (Coefficient of Performance) A thermodynamic device operating in reverse that consumes mechanical work to extract heat from a cold region and reject it into a warmer region. COP_ref = Q_cold / W, COP_hp = Q_hot / W

Reversible Process Thermodynamics & Statistical Physics N/A An idealized thermodynamic process that can be reversed by infinitesimal changes in system variables without leaving any net trace on surroundings. dS_universe = 0

Second Law of Thermodynamics Thermodynamics & Statistical Physics J/K The law asserting that spontaneous physical processes increase total entropy in isolated systems, placing fundamental limits on heat engine efficiency. ΔS_total ≥ 0

Stefan-Boltzmann Law Thermodynamics & Statistical Physics W/m² The physical law asserting that total radiant power emitted per unit surface area of a blackbody is proportional to the fourth power of its absolute thermodynamic temperature. E = σ T⁴, σ = 5.670374 × 10⁻⁸ W/(m²·K⁴)

Sublimation Thermodynamics & Statistical Physics J/kg or J/mol The direct phase transition of a substance from solid to gas state without passing through an intermediate liquid phase. ΔH_sub = ΔH_fus + ΔH_vap

Temperature Thermodynamics & Statistical Physics K (°C, °F) A macroscopic scalar measure of the average translational kinetic energy of constituent particles in a physical system. 1 / T = (∂S / ∂U)_V, E_avg = (3/2) kB T

Thermal Conduction Thermodynamics & Statistical Physics W/m² (k in W/(m·K)) The transfer of thermal energy through a stationary medium via microscopic particle collisions and free electron movement without bulk fluid movement. q = -k A (dT/dx) (Fourier's Law)

Thermal Convection Thermodynamics & Statistical Physics W (h in W/(m²·K)) The transfer of heat energy between a solid surface and an adjacent moving fluid, driven by bulk fluid motion. q = h A (T_surface - T_fluid) (Newton's Law of Cooling)

Thermal Efficiency Thermodynamics & Statistical Physics Dimensionless (%) The dimensionless ratio of net mechanical work produced by a heat engine to total thermal energy input supplied. η = W_net / Q_input = 1 - (Q_out / Q_in)