THRM 200 Lesson 3 - Properties and States

Vocabulary flashcards reviewing key definitions and concepts regarding thermodynamic properties, states, specific properties, path variables, and steady state.

Property

A macroscopic characteristic of a system (piece of matter) that does not in any way depend on the condition of the system at any previous or future point in time, meaning it is path independent and depends only on the final and initial states.

Path Functions

Variables such as mass flow rate ($m$), heat transfer ($Q$), and work transfer ($W$) that are path dependent and depend on the sequence of steps that takes the system from the initial state to the final state.

Intensive Properties

Properties that are independent of the size of the system, whose values may vary with time and position (e.g., temperature, pressure, density).

Extensive Properties

Properties that depend on the size of the system, whose values may vary with time only (e.g., internal energy, mass, volume).

Specific Properties

Extensive properties expressed per unit mass, which are intensive properties and usually denoted with a lowercase variable.

Specific Volume

An intensive specific property defined as volume per unit mass, expressed as $v = \frac{V}{m}$.

Specific Internal Energy

An intensive specific property defined as internal energy per unit mass, expressed as $u = \frac{U}{m}$.

Specific Work

An intensive specific property defined as work per unit mass, expressed as $w = \frac{W}{m}$.

Specific Energy

An intensive specific property defined as total energy per unit mass, expressed as $e = \frac{E}{m}$.

Specific Gravity

A dimensionless quantity defined as the ratio of the density of a substance to the density of water at $4\,^{\circ}\text{C}$ ($\rho_{\text{H}_2\text{O}} = 1000\,\text{kg/m}^3$), calculated as $\text{SG} = \frac{\rho}{\rho_{\text{H}_2\text{O}}}$.

Specific Weight

The weight per unit volume of a substance, calculated as $\gamma_s = \rho g$.

State

The condition of a system (or a piece of matter) as determined by its intensive properties at a particular point in time.

State Postulate for a Pure Substance

The rule stating that the state of a pure substance existing in a single phase within a system is fully defined if just two independent intensive properties are known.

Steady State

The condition of a system in which its properties do not change with time.