Thermodynamics & Statistical Physics — 55 Terms Defined

Adiabatic Process Thermodynamics & Statistical Physics J A thermodynamic process in which no heat is transferred into or out of the system. Q = 0 ⇒ ΔU = -W, P V^γ = constant

Avogadro's Law Thermodynamics & Statistical Physics m³/mol The law stating that equal volumes of all ideal gases at the same temperature and pressure contain equal numbers of molecules. V1 / n1 = V2 / n2 (at constant P, T)

Boyle's Law Thermodynamics & Statistical Physics Pa·m³ An ideal gas law stating that pressure is inversely proportional to volume at constant temperature. P1 V1 = P2 V2 (at constant T)

Brownian Motion Thermodynamics & Statistical Physics m² The random, erratic wandering movement of microscopic particles suspended in a fluid caused by relentless collisions with fast-moving fluid molecules. ⟨x²⟩ = 2 D t, D = kB T / (6 π η r)

Calorimetry Thermodynamics & Statistical Physics J The experimental science and practice of measuring heat energy changes during chemical or physical transformations. Q_lost = Q_gained ⇒ m1 c1 (T1 - T_f) = m2 c2 (T_f - T2)

Carnot Cycle Thermodynamics & Statistical Physics Dimensionless (%) An ideal reversible thermodynamic cycle operating between two thermal reservoirs, establishing maximum theoretical efficiency for heat engines. η_Carnot = 1 - (T_cold / T_hot)

Charles's Law Thermodynamics & Statistical Physics m³/K An ideal gas law stating that gas volume is directly proportional to absolute thermodynamic temperature at constant pressure. V1 / T1 = V2 / T2 (at constant P)

Chemical Potential Thermodynamics & Statistical Physics J/particle (or J/mol) The change in system free energy per added particle at constant temperature and pressure. μ = (∂G / ∂N)_{T,P} = (∂U / ∂N)_{S,V}

Critical Point Thermodynamics & Statistical Physics Pa, K The endpoint of a phase equilibrium curve in a P-T phase diagram where coexisting liquid and vapor phases become indistinguishable. (∂P/∂V)_T = 0, (∂²P/∂V²)_T = 0

Deposition Thermodynamics & Statistical Physics J/kg or J/mol The direct phase transition of a gas into a solid without passing through an intermediate liquid phase. ΔH_dep = -ΔH_sub

Emissivity Thermodynamics & Statistical Physics Dimensionless The dimensionless ratio of thermal energy radiated by a surface to that radiated by an ideal blackbody at the exact same temperature. ε = E_surface / E_blackbody (0 ≤ ε ≤ 1)

Enthalpy Thermodynamics & Statistical Physics J A thermodynamic potential defined as internal energy plus the product of pressure and volume, representing total heat content under constant pressure conditions. H = U + P V, ΔH = Q_p

Entropy Thermodynamics & Statistical Physics J/K A fundamental thermodynamic property measuring the degree of microscopic disorder, randomness, or thermal energy unavailable for mechanical work in a system. dS = dQ_rev / T, S = kB ln Ω

Equipartition Theorem Thermodynamics & Statistical Physics J A classical statistical mechanics theorem stating that every independent quadratic degree of freedom contributes ½ kB T to a system's average energy in thermal equilibrium. E_avg = (f / 2) kB T

First Law of Thermodynamics Thermodynamics & Statistical Physics J A statement of universal energy conservation applied to thermodynamic systems, asserting that internal energy change equals net heat added minus work done by the system. ΔU = Q - W

Gay-Lussac's Law Thermodynamics & Statistical Physics Pa/K An ideal gas law stating that gas pressure is directly proportional to absolute thermodynamic temperature at constant volume. P1 / T1 = P2 / T2 (at constant V)

Gibbs Free Energy Thermodynamics & Statistical Physics J A thermodynamic potential measuring maximum reversible work obtainable from a system at constant temperature and pressure. G = H - T S, ΔG = ΔH - T ΔS

Graham's Law of Effusion Thermodynamics & Statistical Physics mol/s or m³/s The law stating that rate of effusion or diffusion of a gas is inversely proportional to square root of its molar mass. Rate1 / Rate2 = √(M2 / M1)

Heat Engine Thermodynamics & Statistical Physics W (J/s) A physical device that converts thermal energy absorbed from a high-temperature heat source into mechanical work, discharging waste heat to a cold sink. W = Q_hot - Q_cold, η = W / Q_hot

Helmholtz Free Energy Thermodynamics & Statistical Physics J A thermodynamic potential measuring maximum reversible work obtainable from a closed system at constant temperature and volume. F = U - T S, dF = -S dT - P dV

Ideal Gas Law Thermodynamics & Statistical Physics Pa·m³ = J The equation of state relating pressure, volume, temperature, and quantity of an ideal gas composed of non-interacting point particles. P V = n R T = N kB T

Intensive vs Extensive Properties Thermodynamics & Statistical Physics Various Classification of thermodynamic properties based on whether they depend on system size or amount of matter. Extensive: U, V, S, m, H; Intensive: T, P, ρ, μ

Internal Energy Thermodynamics & Statistical Physics J The total microscopic energy contained within a thermodynamic system, comprising kinetic energies of particle translational/rotational/vibrational motion and potential energies of intermolecular forces. U = (f/2) n R T (for ideal gas)

Isobaric Process Thermodynamics & Statistical Physics J A thermodynamic change in state occurring under constant pressure conditions. ΔP = 0, W = P ΔV, Q = ΔH = n Cp ΔT