Thermodynamics, Enthalpy, and Heat Capacity

Vocabulary practice flashcards covering internal energy, pressure-volume work, enthalpy changes, phase change enthalpies, specific heat, and heat capacity based on the lecture.

Internal Energy Change ($\Delta U$)

The total change in energy of a system, governed by the first law equation $\Delta U = q + w$, where $q$ is heat and $w$ is work.

Pressure-Volume Work ($w$)

The mechanical work done by or on a system due to expansion or compression against an external pressure, defined as $w = -P\Delta V$.

Enthalpy Change ($\Delta H$)

The heat of reaction transferred at constant pressure ($q_p$), defined mathematically as $\Delta H = \Delta U + P\Delta V$.

State Function

A property whose value depends solely on the current state of the system, not on the specific pathway taken to reach that state.

Exothermic Reaction

A chemical reaction with a negative enthalpy change ($\Delta H < 0$), indicating that heat flows out of the system into the surroundings.

Endothermic Reaction

A chemical reaction with a positive enthalpy change ($\Delta H > 0$), indicating that heat flows into the system from the surroundings.

Enthalpy of Fusion ($\Delta H_{\text{fus}}$;)

The quantity of heat required to melt a substance from a solid to a liquid without changing its temperature.

Enthalpy of Vaporization ($\Delta H_{\text{vap}}$;)

The quantity of heat required to vaporize a substance from the liquid state to the gaseous state without changing its temperature.

Enthalpy of Sublimation ($\Delta H_{\text{sub}}$;)

The quantity of heat required to convert a substance directly from the solid phase to the gas phase without passing through the liquid phase.

$RT\Delta n$ Substitution

An expression derived from the ideal gas law ($PV = nRT$) used to substitute for $P\Delta V$ in gas reactions, giving $\Delta U = \Delta H - RT\Delta n$.

Specific Heat ($c$)

The quantity of heat necessary to raise the temperature of $1\,\text{g}$ of a substance by $1\,^\circ\text{C}$ (or $1\,\text{K}$).

Heat Capacity ($C$)

The quantity of heat required to raise the temperature of an entire object or sample, calculated as mass times specific heat ($C = m \times c$).

Extensive Property

A physical or thermodynamic property, such as heat capacity, that depends directly on the sample size.