Applied Chemistry: Thermodynamics Vocabulary

A comprehensive set of vocabulary flashcards covering the fundamental thermodynamic concepts introduced in the Applied Chemistry lecture notes.

Thermodynamics

Branch of science that describes how thermal energy is converted from one form to another and how it affects matter.

System

The specified portion of the universe chosen for study in thermodynamics.

Surroundings

Everything external to the system being studied.

Boundary

The real or imaginary surface that separates a system from its surroundings.

Open System

A system that exchanges both mass and heat with its surroundings.

Closed System

A system that exchanges heat but not mass with its surroundings.

Isolated System

A system that exchanges neither heat nor mass with its surroundings.

Intensive Property

Property that does not depend on the amount of matter present, e.g., temperature or pressure.

Extensive Property

Property that depends on the amount of matter present, e.g., volume or internal energy.

State Function

Property that depends only on the initial and final states of a system, not on the path taken.

Path Function

Property that depends on the specific path taken between two states, e.g., work or heat.

Internal Energy (U)

Sum of the kinetic and potential energies of all particles in a system; a state function.

Work (w)

Energy transfer due to force acting through a distance, defined in thermodynamics as w = −P_ext dV for expansion/compression.

Heat (q)

Energy transfer due to temperature difference between a system and its surroundings.

Zeroth Law of Thermodynamics

If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

First Law of Thermodynamics

Law of conservation of energy: ΔU = q − w for a closed system.

Second Law of Thermodynamics

Entropy of an isolated system increases in any spontaneous process (ΔS_tot > 0).

Third Law of Thermodynamics

Entropy of a perfect crystal approaches zero as temperature approaches absolute zero (0 K).

Enthalpy (H)

Thermodynamic quantity defined as H = U + PV; useful at constant pressure.

Heat Capacity (C)

Amount of heat required to raise a system’s temperature by one degree (C = q/ΔT).

Specific Heat Capacity

Heat capacity per unit mass (C = q/mΔT).

Molar Heat Capacity

Heat capacity per mole of substance.

Cv (Heat Capacity at Constant Volume)

Molar heat capacity measured when volume is held constant; for ideal monatomic gas, Cv = 3/2 R.

Cp (Heat Capacity at Constant Pressure)

Molar heat capacity measured when pressure is held constant; for ideal monatomic gas, Cp = 5/2 R.

Heat Capacity Ratio (γ)

Ratio of Cp to Cv (γ = Cp/Cv).

Isothermal Process

Thermodynamic process that occurs at constant temperature (ΔT = 0).

Adiabatic Process

Process in which no heat is exchanged with surroundings (q = 0).

Isobaric Process

Process that occurs at constant pressure (P = constant).

Isochoric Process

Process that occurs at constant volume (V = constant); work done is zero.

Reversible Process

Idealized process that can be reversed with no net change to system or surroundings.

Irreversible Process

Real process that cannot return both system and surroundings to original states without changes elsewhere.

Free Expansion

Adiabatic expansion against zero external pressure; w = 0 and q = 0.

Carnot Cycle

Idealized four-step reversible cycle (two isothermal, two adiabatic) that sets the maximum efficiency for heat engines.

Heat Engine

Device that converts heat into work while operating in a cycle between two reservoirs.

Carnot Efficiency (η)

Maximum possible efficiency of a heat engine: η = 1 − TC/TH (temperatures in Kelvin).

Entropy (S)

State function that measures dispersal of energy; defined differentially as dS = dq_rev/T.

Clausius Inequality

For any real (irreversible) cycle, ∮dq/T < 0, reflecting entropy production.

Helmholtz Free Energy (A)

State function A = U − T S; criterion for spontaneity at constant volume and temperature (ΔA ≤ 0).

Gibbs Free Energy (G)

State function G = H − T S; criterion for spontaneity at constant pressure and temperature (ΔG ≤ 0).

Gibbs–Helmholtz Equation

Relation ΔG = ΔH − TΔS connecting free energy, enthalpy, entropy, and temperature.

Spontaneous Process

Process that occurs without external intervention; characterized by ΔG < 0 under constant T and P.

Kelvin (Thermodynamic) Temperature Scale

Absolute temperature scale based on the efficiency limit of reversible heat engines; 0 K is absolute zero.

Heat Pump

Device that transfers heat from a colder body to a hotter one by doing work; refrigeration is the same cycle used for cooling.

Refrigeration Cycle

Reverse Carnot-type cycle that absorbs heat at low temperature and rejects it at higher temperature to provide cooling.

Free Energy–Temperature Relationship

For reactions where ΔH and ΔS have the same sign, temperature dictates whether ΔG is negative (spontaneous).