Thermodynamics Fundamentals: Basic Concepts and Definitions

Vocabulary practice flashcards covering fundamental thermodynamic definitions, system classifications, properties, equilibrium types, processes, cycles, energy forms, pressure, and the Zeroth Law of Thermodynamics from Week 5 lecture notes.

Thermodynamics

The branch of science that deals with energy, how it transforms, and the properties of matter, originating from the Greek words therme (heat) and dynamis (power) from early efforts to convert heat into work.

First Law of Thermodynamics

The principle of conservation of energy, which asserts that energy cannot be created or destroyed; it can only change forms.

Second Law of Thermodynamics

A fundamental law stating that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy.

Classical (Macroscopic) Approach

A direct method of solving engineering problems using systems-level analysis that does not require knowledge of the behavior of individual particles.

Thermodynamic System

A quantity of matter or a specific region in space chosen for study.

Surroundings

Everything located external to the system boundary.

Boundary

The real or imaginary surface that separates a system from its surroundings, which can be fixed or movable.

Closed System (Control Mass)

A system containing a fixed quantity of mass, across whose boundary no mass can enter or leave, though energy (heat or work) can cross and volume may change.

Isolated System

A special type of closed system where neither mass nor energy is allowed to cross the boundary.

Control Volume (Open System)

A selected region in space (typically enclosing a device) where mass and energy can flow into, out of, or through the system boundary (control surface).

Triple Point

The unique set of temperature and pressure conditions at which the solid, liquid, and vapor phases of a substance coexist in thermodynamic equilibrium.

Triple-Point Cell

A sealed glass vessel containing water of a specific isotopic composition used with a platinum-resistance thermometer to provide a precise reference temperature of $273.16\,K$ ($0.01\,^\circ\text{C}$).

Thermodynamic Properties

Measurable characteristics of a system (such as mass, volume, pressure, temperature, and internal energy) that define its state. Process-dependent quantities like heat and work are not properties.

Extensive Properties

Properties whose values depend on the size or extent of the system, such that the value of the overall system is the sum of the values of its individual parts (e.g., mass, volume, energy).

Intensive Properties

Properties that are independent of the size or mass of the system and are non-additive (e.g., temperature, pressure, density).

Specific Properties

Intensive properties defined as extensive properties expressed per unit mass of a system, such as specific volume ($\nu = \frac{V}{m}$) or specific internal energy ($u = \frac{U}{m}$).

Specific Gravity ($SG$)

A dimensionless ratio of the density of a substance to the density of standard fresh water: $SG = \frac{\rho}{\rho_{\text{fresh\_water}}}$.

Specific Weight ($\gamma_s$)

The weight of a unit volume of a substance, calculated as $\gamma_s = \rho \cdot g$, with water having a standard value of approximately $9.807\,\text{kN/m}^3$.

State

The specific condition of a system at an instant in time, completely described by a sufficient set of properties and entirely independent of the past path or history of the system.

Thermal Equilibrium

A condition in which the temperature is uniform throughout the system, meaning there is no temperature gradient and no net transfer of heat.

Mechanical Equilibrium

A condition of force and pressure balance throughout a system, meaning there is no change in pressure at any point with time.

Phase Equilibrium

A state in which two or more phases of a substance coexist without any net change in the mass of each phase over time.

Chemical Equilibrium

A condition where the chemical composition of a system does not change over time and no further chemical potential gradients exist.

State Postulate

The principle stating that the thermodynamic state of a simple compressible system is completely specified by two independent, intensive properties.

Simple Compressible System

A system that is free from external electrical, magnetic, gravitational, motion, and surface tension effects.

Thermodynamic Process

Any transformation that changes a system from one equilibrium state to another, characterized by an initial state, a final state, and a process path.

Reversible Process

An idealized process where both the system and its surroundings can be returned to their initial states simply by reversing the direction of the process.

Thermodynamic Cycle

A series of thermodynamic processes that starts and finishes at the exact same equilibrium state, resulting in a net property change of zero.

Quasi-Equilibrium Process

A sufficiently slow, idealized process during which the system remains infinitesimally close to an equilibrium state at all times.

Isothermal Process

A thermodynamic process carried out at a constant temperature ($T = \text{constant}$).

Isobaric Process

A thermodynamic process carried out at a constant pressure ($P = \text{constant}$).

Isochoric (Isometric) Process

A thermodynamic process carried out at a constant specific volume or volume ($\nu = \text{constant}$).

Adiabatic Process

A process in which no heat is transferred into or out of the system across the boundary ($Q = 0$).

Steady-Flow Process

A process during which a fluid flows steadily through a control volume such that the total mass and energy within the control volume remain constant over time.

Total Energy ($E$)

The sum of all macroscopic energy forms (kinetic energy $KE$ and potential energy $PE$) and microscopic energy forms (internal energy $U$): $E = KE + PE + U$.

Internal Energy ($U$)

The sum of all microscopic forms of energy associated with the structure, rotation, translation, vibration, chemical bonding, and nuclear forces of a system's molecules.

Absolute Pressure ($P_{\text{abs}}$)

The actual pressure of a fluid measured relative to absolute zero pressure (a perfect vacuum).

Gauge Pressure ($P_{\text{gage}}$)

The pressure measured relative to local atmospheric pressure: $P_{\text{gage}} = P_{\text{abs}} - P_{\text{atm}}$.

Vacuum Pressure ($P_{\text{vac}}$)

Pressure below local atmospheric pressure, calculated as $P_{\text{vac}} = P_{\text{atm}} - P_{\text{abs}}$.

Zeroth Law of Thermodynamics

A fundamental law stating that if two bodies are each in thermal equilibrium with a third body, they are also in thermal equilibrium with each other, establishing the basis for temperature measurement.