Thermodynamics and Chemical Equilibrium Flashcards

Comprehensive vocabulary flashcards covering the fundamental laws, state functions, mathematical derivations, and equilibrium principles of chemical thermodynamics (Lectures 10 through 16).

Thermodynamics

The study of energy, enthalpy, entropy, and free energy, and their relationships with heat, work, and temperature.

System

The specific part of the universe being studied, such as $1\,\text{L}$ of water, $1\,\text{mol}$ of $\text{H}_2 + 1\,\text{mol}$ of $\text{O}_2$, or $n\,\text{mol}$ of helium.

Surroundings

Everything in the universe outside of the system being studied ($\text{Universe} = \text{System} + \text{Surroundings}$).

Internal Energy ($E$)

The total sum of kinetic energy ($\text{KE}$) and potential energy ($\text{PE}$) of all particles or matter within a system ($E = \text{KE} + \text{PE}$).

First Law of Thermodynamics

The principle stating that the total energy of the universe is conserved, meaning the internal energy of a system changes exclusively via heat ($q$) and work ($w$): $\Delta E = q + w$.

Heat ($q$)

Energy transferred between a system and its surroundings due to a temperature difference; designated positive ($+$") when heat enters the system and negative ("$\text{–}$") when heat leaves the system.

Work ($w$)

Energy transferred between a system and its surroundings through an unbalanced force acting across a distance; defined for gas expansion or compression as $w = -P_{ext}\Delta V$.

State Function

A property whose value depends solely on the current equilibrium state (initial and final states) of the system, completely independent of the pathway taken to reach it (e.g., $E$, $H$, $S$, and $G$).

Path Function

A property whose numerical value depends directly on the specific path or mechanism taken between the initial and final states (e.g., heat $q$ and work $w$).

Exothermic Process

A thermodynamic change in which energy as heat or work is released from the system to the surroundings ($\Delta E < 0$ or $\Delta H < 0$).

Endothermic Process

A thermodynamic change in which energy as heat or work is absorbed by the system from the surroundings ($\Delta E > 0$ or $\Delta H > 0$).

Enthalpy ($H$)

A state function defined mathematically as $H = E + PV$, which equates to the heat exchanged with the surroundings during a constant-pressure process ($q_p = \Delta H$).

Monatomic Ideal Gas

A theoretical gas composed of non-interacting, single atoms whose internal energy consists entirely of translational kinetic energy ($E = \frac{3}{2}RT$ for $1\,\text{mol}$) and depends exclusively on temperature ($T$).

Extensive Property

A physical or chemical characteristic whose value is directly proportional to the amount or size of matter in a given sample (e.g., $E$, $H$, $S$, $G$).

Molar Heat Capacity ($C$)

The amount of energy transferred as heat required to raise the temperature of $1\,\text{mol}$ of a substance by $1\,\text{K}$ ($C = \frac{q}{\Delta T}$).

Constant-Volume Molar Heat Capacity ($C_v$)

The heat capacity of a substance measured at constant volume ($C_v = \frac{\Delta E}{\Delta T}$), equal to $\frac{3}{2}R$ for a monatomic ideal gas.

Constant-Pressure Molar Heat Capacity ($C_p$)

The heat capacity of a substance measured at constant pressure ($C_p = \frac{\Delta H}{\Delta T}$), equal to $\frac{5}{2}R$ for a monatomic ideal gas, and consistently larger than $C_v$ by $R$ ($C_p - C_v = R$) for all ideal gases.

Specific Heat Capacity ($c$)

The quantity of energy transferred as heat required to raise the temperature of $1\,\text{g}$ of a substance by $1^\circ\text{C}$ (or $1\,\text{K}$), expressed in $\text{J}\,\text{K}^{-1}\,\text{g}^{-1}$.

Hess's Law

The principle stating that if a reaction is carried out in a series of steps, the overall enthalpy change ( $\Delta H_{rxn}^\circ$ ) equals the sum of the enthalpy changes for each individual step.

Standard State ($^\circ$)

The defined thermodynamic reference state: $1\,\text{atm}$ for gases, $1\,\text{M}$ at $1\,\text{atm}$ for dissolved species, and the most stable physical form of a pure element or compound at $1\,\text{atm}$ and $25^\circ\text{C}$.

Standard Heat of Formation ($\Delta H_f^\circ$)

The enthalpy change occurring when $1\,\text{mol}$ of a compound forms from its constituent elements in their standard states; defined as zero for pure elements in their standard states.

Bond Dissociation Energy ($D$)

The quantity of energy required to break a chemical bond in the gas phase; bond breaking is endothermic while bond formation is exothermic.

Spontaneous Process

A physical or chemical change that occurs naturally under specified conditions without needing continuous input of work from an external source.

Entropy ($S$)

A thermodynamic state function that serves as a quantitative measure of the disorder, randomness, or microstate dispersal of a system.

Boltzmann Entropy Formula

The statistical equation $S = k_B\ln(\Omega)$, which links macroscopic entropy to microscopic states, where $k_B = 1.38 \times 10^{-23}\,\text{J}\,\text{K}^{-1}$ and $\Omega$ is the number of accessible microstates.

Second Law of Thermodynamics

The fundamental principle establishing that the total entropy of the universe always increases or remains constant in any spontaneous process ($\Delta S_{univ} = \Delta S_{sys} + \Delta S_{surr} \ge 0$).

Reversible Process

A hypothetical, infinitely slow process occurring through continuous equilibrium states, in which the system and surroundings can be returned to their exact original states with no net change in the universe.

Third Law of Thermodynamics

The law stating that the entropy of a perfect crystal of a pure substance approaches zero as temperature approaches absolute zero ($S = 0$ at $T = 0\,\text{K}$).

Standard Molar Entropy ($S^\circ$)

The absolute entropy gained by $1\,\text{mol}$ of a substance when heated from $0\,\text{K}$ to $298\,\text{K}$ at a constant pressure of $1\,\text{atm}$.

Gibbs Free Energy ($G$)

A thermodynamic function defined as $G = H - TS$, used to evaluate reaction spontaneity at constant temperature and pressure ($\Delta G = -T\Delta S_{univ}$).

Spontaneity Conditions (Gibbs Free Energy)

The temperature and sign criteria governing reaction spontaneity: spontaneous at all $T$ when $\Delta H < 0$ and $\Delta S > 0$; nonspontaneous at all $T$ when $\Delta H > 0$ and $\Delta S < 0$; spontaneous at low $T$ when both are negative; spontaneous at high $T$ when both are positive.

Turnover Temperature ($T^*$)

The threshold temperature at which $\Delta G^\circ = 0$, marking the transition point between spontaneity and non-spontaneity ($T^* = \frac{\Delta H^\circ}{\Delta S^\circ}$).

Standard Gibbs Free Energy of Formation ($\Delta G_f^\circ$)

The change in Gibbs free energy accompanying the formation of $1\,\text{mol}$ of a substance from its constituent elements in standard states at $1\,\text{atm}$ and $25^\circ\text{C}$.

Chemical Equilibrium (Free Energy Perspective)

The thermodynamic point along a reaction coordinate where total Gibbs free energy reaches its lowest possible value and $\Delta G = 0$.

Reaction Quotient ($Q$)

The ratio of product concentrations or partial pressures to reactant concentrations or partial pressures, each raised to their stoichiometric coefficients, evaluated at any given instant during a reaction.

Equilibrium Constant ($K$)

The fixed numerical value assumed by the reaction quotient $Q$ when a system reaches dynamic equilibrium at a specified temperature, governed by $\Delta G^\circ = -RT\ln(K)$.

Equilibrium Position

A specific set of equilibrium concentrations or partial pressures of reactants and products satisfying the constant $K$ at a given temperature, which lies closer to products if $\Delta G^\circ < 0$ ($K > 1$) and closer to reactants if $\Delta G^\circ > 0$ ($K < 1$).

van 't Hoff Equation

The thermodynamic equation $\ln(K) = -\frac{\Delta H^\circ}{R}\left(\frac{1}{T}\right) + \frac{\Delta S^\circ}{R}$, which describes how the equilibrium constant $K$ changes as a function of temperature.

Useful Work ($w_{max,useful}$)

The non-expansion mechanical, electrical, or chemical work that can be extracted from a system; constrained at constant temperature and pressure by $\Delta G = w_{max,useful}$.

Le Chatelier's Principle

The principle stating that if a chemical system at equilibrium experiences an external perturbation (such as a change in concentration, pressure, volume, or temperature), the system shifts in a direction that minimizes the disturbance to re-establish equilibrium.

Partial Pressure

The pressure that a specific gas component in a mixture would exert if it alone occupied the entire volume of the container at the same temperature.

Haber-Bosch Process

An industrial exothermic process for synthesizing ammonia from nitrogen and hydrogen gases, operating at high pressures and an optimized compromised temperature of approximately $500^\circ\text{C}$ to balance yield with reaction kinetics.