Thermodynamics - Heat, Temperature, and Scales

Vocabulary flashcards covering core thermodynamics concepts, including internal and thermal energy, heat, temperature, heat transfer processes, temperature scales, fixed points, thermometry, and thermal expansion.

Internal Energy ($U$)

The sum of the kinetic energy and potential energy of all molecules within matter, represented as $U = \text{thermal energy} + \text{bond energy}$.

Thermal Energy

The total present net disordered kinetic energy resulting from the random movements (rotational, vibrational, translational) of atoms and molecules in a system.

Heat

Thermal energy in transit that is transferred, via atomic collisions, from a region of higher temperature to a region of lower temperature.

Temperature

A measure of the average kinetic energy of the molecules that make up an object, independent of the total number of atoms present.

Thermal Equilibrium

The state of two or more bodies in thermal contact where they are at the same temperature and there is no net flow of heat energy between them.

Zeroth Law of Thermodynamics

The physical law stating that when two bodies A and B are each in thermal equilibrium with a third body C, then A and B are in thermal equilibrium with each other.

Convection

A heat transfer process in which energy is transferred from one body to a cooler one via currents in a fluid (a gas or liquid).

Radiation

A heat transfer process where objects emit and absorb electromagnetic radiation, requiring no physical medium.

Conduction

A heat transfer process occurring primarily in solids where energy is transferred through direct contact as faster-moving molecules bump into neighboring cooler molecules.

Fourier's Law of Heat Conduction

The law stating that the rate of heat transfer by conduction is given by $\frac{Q}{t} = k A \left(\frac{\Delta T}{L}\right)$, where $k$ is thermal conductivity, $A$ is cross-sectional area, $\Delta T$ is temperature gradient, and $L$ is length.

Fixed Point

A single specific temperature at which a particular physical event always reliably occurs under standard conditions.

Ice Point

The fixed temperature at which ice can exist in thermal equilibrium with water at standard atmospheric pressure ($0\,^\circ\text{C}$ or $273.15\,\text{K}$).

Steam Point

The fixed temperature at which pure water can exist in thermal equilibrium with its water vapor at standard atmospheric pressure ($100\,^\circ\text{C}$ or $373.15\,\text{K}$).

Absolute Zero Point

The temperature at $-273.15\,^\circ\text{C}$ ($0\,\text{K}$) at which no movement of individual atoms or molecules occurs and an ideal gas exerts no pressure.

Triple Point of Water

The unique temperature-pressure combination ($0.01\,^\circ\text{C}$ / $273.16\,\text{K}$ and $4.58\,\text{mm Hg}$) at which solid ice, liquid water, and water vapor coexist in equilibrium.

Constant-Volume Gas Thermometer

A thermometer setup that measures temperature by reading gas pressure changes at a fixed volume based on Gay-Lussac's law ($P \propto T$).

Thermometry

The science and practical methodology of measuring temperature.

Thermometric Property

A physical property of a substance (such as length, volume, pressure, or electrical resistance) that changes measurably as a function of temperature.

Thermometer

An object or system possessing a measurable property that varies in a reliable, reproducible, and monotonic way as a function of temperature.

Thermocouple

A temperature sensor consisting of a junction between two dissimilar metals that generates a temperature-dependent voltage across the junction via the thermoelectric effect.

Thermal Expansion

The tendency of matter to change its dimensions (such as length or volume) in response to a temperature change due to alterations in average atomic separation.