CHEM 502: Chemical Thermodynamics and Kinetics

Vocabulary practice flashcards covering chemical thermodynamics, laws of thermodynamics, internal energy, enthalpy, phase transitions, entropy, and Gibbs free energy.

First Law of Thermodynamics

The law stating that energy cannot be created or destroyed, only transferred from one location to another or converted from one form to another, expressed mathematically as $\Delta U = q + w$.

System

The specific region or part of the physical universe where chemical reactions or processes are actively occurring.

Surroundings

The immediate area and environment located around the system that can interact with it.

Universe (Thermodynamics)

The wider expanse comprising both the system and the surroundings combined.

State Function

A property of a system that depends only on its current state and intrinsic conditions, rather than on the pathway taken to reach that state (e.g., temperature, volume, internal energy, enthalpy, and entropy).

Internal Energy ($U$)

A thermodynamic state function that represents the sum total of all the energies of all particles within a system, altered via heat ($q$) and work ($w$).

Heat ($q$)

Energy transferred into or out of a system that changes internal energy by changing the population of particles among ground and excited energy levels.

Endothermic Process

A thermodynamic process where heat is transferred from the surroundings into the system ($q > 0$, $\Delta H > 0$), increasing system internal energy while decreasing surroundings energy.

Exothermic Process

A thermodynamic process where heat is released from the system towards the surroundings ($q < 0$, $\Delta H < 0$), decreasing the internal energy of the system while increasing the energy of the surroundings.

Work ($w$)

Energy transfer between systems that differs from heat (such as mechanical compression or expansion) by physically moving the energy levels themselves up or down.

Heat Capacity ($C$)

The quantity of heat energy required to increase the temperature of $1\,g$ of a substance by $1$ degree ($1\,^{\circ}\text{C}$ or $1\,K$), defined by the relation $q = C\Delta T$.

Pressure-Volume Work ($w$)

Mechanical work resulting from the expansion or compression of a system against an external pressure, calculated as $w = -p \times \Delta V$.

Calorimeter

An experimental apparatus operating as a closed system at constant pressure (typically constructed with nested Styrofoam cups, a lid, a stirrer, and a thermometer) to determine heat changes and enthalpy via $\Delta H = q = mc\Delta T$.

Enthalpy ($H$)

A thermodynamic quantity accounting for internal energy, pressure, and volume ($H = U + PV$); at constant pressure, the change in enthalpy equals heat exchange ($\Delta H = q$).

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

The endothermic heat change ($\Delta H > 0$) absorbed by a liquid system as it transitions into a gas ($\Delta H_{vaporization} = H_{vap} - H_{liquid}$), causing intermolecular separation to increase.

Enthalpy of Condensation ($\Delta H_{cond}$)

The exothermic heat change ($\Delta H < 0$) released as a gas transforms into a liquid ($\Delta H_{condensation} = H_{liquid} - H_{vapour}$), equal in magnitude and opposite in sign to the enthalpy of vaporization.

Enthalpy of Fusion ($\Delta H_{fusion}$)

The endothermic heat absorbed ($\Delta H > 0$) during the phase change from solid to liquid, yielding disorganized molecules that can rotate as well as vibrate.

Enthalpy of Sublimation ($\Delta H_{sublimation}$)

The enthalpy change for the direct transition from solid to gas, equivalent to the sum of the enthalpy of fusion and the enthalpy of vaporization.

Phase Diagram

A pressure-temperature plot showing the phase boundaries of solid, liquid, and vapour, displaying the triple point ($T$) where all three coexist and the critical point ($C$).

Hess's Law

The principle stating that if a reaction or state change from state A to state B occurs in multiple steps, the total change in any state function (such as $\Delta H$ or $\Delta T$) is the sum of the individual step changes.

Second Law of Thermodynamics

The principle stating that the entropy of the universe will always increase over time, and all spontaneous reactions lead to an increase in total entropy ($\Delta S_{universe} = \Delta S_{sys} + \Delta S_{surr} > 0$).

Entropy ($S$)

A state function associated with disorder that measures the statistical distribution of energy among particles, typically decreasing in the order $\text{gas} > \text{liquid} > \text{solid}$.

Gibbs Free Energy ($G$)

A thermodynamic property defined as $\Delta G = \Delta H - T\Delta S$, where a negative $\Delta G$ indicates a spontaneous process and a positive $\Delta G$ indicates a non-spontaneous process.

Standard Enthalpy of Formation ($\Delta H_f^{\circ}$)

The enthalpy change when one mole of a compound is synthesized from its reference elements under standard conditions ($1 \times 10^5\,Pa$, typically reported at $298\,K$ / $25.0\,^{\circ}\text{C}$).

Gibbs–Temperature (GT) Graph

A plot of Gibbs free energy against temperature ($G = H - TS$) used to identify the most stable species or state across different temperatures, where the state with the lowest Gibbs free energy is favored.