Important Thermo Terms

For CHE 304

Energy

A characteristic (or property) of a finite material body in equilibrium with its surroundings that gives it the capacity to convey some portion of this characteristic via thermal (heat) and/or mechanical (work) means to its immediate surroundings (or vice versa).

Heat

Transfer of thermal energy from a system at a higher temp to a lower temp (temperature differential)

Not a property

Work

The changes of the thermodynamic system's own internal state variables, such as volume

A form of energy transfer like heat

Not a property

System

Is any object, or finite quantity of matter that occupies a region of space that is selected to be set aside for study.

Subsystem

A sub-system is obtained when a thermodynamic system is divided into two or more sub-parts separated by a sub-system boundary

Surroundings

The portion that is not in the system

Only includes the portion immediate space outside of the system that is capable of interacting with it

System Boundary

A distinct physical and/or chemical boundary (or interface) forms at the periphery of the system and separates the system from its surroundings.

May or May NOT allow for the surroundings to interact with the system

Universe

Includes both the system and surroundings

Phase of Matter

The standard solid, liquid, and gas

Pure Phases have distinct molecular arrangement and chemistry

Thermodynamic property

A macroscopic characteristic of a finite body of matter that describes the internal state of the system and to which a specific numerical value can be assigned without knowledge or reference to its previous history.

Example: Pressure, Volume, Temperature

Absolute Property

A property that does not depend on a choice of reference state

Example: Density, Thermal expansion, Compressibility, Heat capacity, Electical conductivity

Floating Property

Properties that cannot be measured directly but must be computed relative some arbitrarily assigned reference condition.

Depends on choice of reference state

Example: Internal energy, Enthalpy, Entropy, Gibbs free energy

Intensive Property

Properties that are independent of the size of the system and may vary from place to place within the system at any moment of time

Examples: Pressure, Density, Temperature, Heat Capacity, Enthalpy

Extensive Property

Properties dependent on the size of the system

Examples: Volume, Area, Mass

Non-Property

A quantity or characteristic that changes in value between 2 states but is dependent on the process used rather the end states themselves

Thermodynamic State

A body’s sum totality of all its properties

Described as a subset of properties from which other properties can be determined.

Control Property

Properties which can be externally prescribed to alter the energy state of a materials system

Examples: Pressure, Temperature, Volume, Chemical Composition

Dependent Property

Properties that are determined (or dependent on) the setting of the controllable properties

Examples: Internal energy, enthalpy, entropy, free energy, Heat capacity (at const T or V)

Macrostate

Any state where the thermodynamic properties can be easily measured using laboratory equipment

Microstate

Any state where the thermodynamic properties are determined by microscopic quantum mechanical parameters.

Macroscopic system

A system that is treated as treated as a whole unit

The parameters that describe the system must apply to system as a whole

Microscopic system

A system treated as a collection of minute atomic/molecular discrete entities.

System variables apply only to individual particles

Equation of State (EOS)

Mathematical relationships that exist among the thermodynamic properties

Examples: Ideal Gas Law Equations binding P,V,T together

Open System

A system which not only thermal and mechanical energy can contact with its surroundings but also will allow the passage of matter through it.

Closed System

A system which thermal or mechanical energy can contact with its surroundings but does not allow the passage of matter into or out of it.

Isolated System

A system which thermal or mechanical energy and physical matter cannot contact with the surroundings.

Equilibrium

A state of matter in which all the forces acting on a system are in balance

Mechanical Equilibrium

No unbalanced forces acting on the system

Another Name: (Hydrostatic)

Thermal Equilibrium

No temperature gradients throughout system

System must be at uniform temperature

No net heat flow between different systems

Chemical Equilibrium

No chemical reactions take place at measurable rates

Rate of forward reactions = rate of reverse reactions

Phase Equilibrium

Two or more different phases of matter (solid, liquid, vapor) co-exist at a given P and T

Path

A specific pre-selected process whereby a system changes its properties according to a prescribed set of parameters that describe this.

An open one does not allow the system to return to its original starting state

A closed one allows the system to return to its original starting point (Reversible)

Constraint

A thermodynamic property that is fixed at a pre-selected value and the thermodynamic process is carried out with this fixed value throughout.

Examples: Constant Temp, Pressure, Volume

Infinitesimal Process

A process carried out such that only very small changes in thermodynamic coordinates can occur

Examples: dT, dV, dP

Finite Process

Takes place where fixed changes in thermodynamic coordinates can be measured

Examples: ΔT, ΔP, ΔV

Quasi-Static Process

A process carried out so slowly that the system is always close to thermal, mechanical or chemical equilibrium

Examples: slow withdrawal of a frictionless piston inside piston-cylinder assembly containing a gas

Isothermal Process

Process carried out such that the system temperature remains constant throughout

Adiabatic Process

Process carried out such that no heat is allowed to enter or escape the system

Isobaric Process

Process carried out such that the system pressure remains constant throughout

Isometric Process

Process carried out at constant volume

Reversible Process

A process is one in which a system and all parts of the surroundings can be restored to their initial states after a given process is reversed along the same path.

Irreversible Process

A process is one in which the system or surroundings (or both) are permanently changed when the process is reversed from the final to initial state.