Chemical Equilibrium, Le Chatelier's Principle, and Thermodynamics Flashcards

Vocabulary flashcards reviewing chemical equilibrium shifts, Le Chatelier's principle, the Van 't Hoff equation, free energy relationships, and phase transitions.

Le Chatelier's Principle

The principle stating that if a stress is applied to a system at equilibrium, the system will shift in a direction that relieves the applied stress.

Van 't Hoff Equation

The quantitative version of Le Chatelier's principle connecting the equilibrium constant ($K$) to temperature ($T$) and standard enthalpy of reaction ($\Delta H_{\text{rxn}}$), expressed as $\ln\left(\frac{K_2}{K_1}\right) = -\frac{\Delta H_{\text{rxn}}}{R}\left(\frac{1}{T_2} - \frac{1}{T_1}\right)$.

Endothermic Reaction Equilibrium Shift

A reaction where $\Delta H > 0$; increasing temperature ($T$) shifts the equilibrium to the right toward products, resulting in an increased equilibrium constant ($K_2 > K_1$ when $T_2 > T_1$).

Exothermic Reaction Equilibrium Shift

A reaction where $\Delta H < 0$; increasing temperature ($T$) shifts the equilibrium to the left toward reactants, resulting in a decreased equilibrium constant ($K_2 < K_1$ when $T_2 > T_1$).

Standard Gibbs Free Energy and Equilibrium Constant Equation

The mathematical relationship $\Delta G^\circ = -RT \ln(K)$, derived from $\Delta G = \Delta G^\circ + RT \ln(Q)$ at equilibrium where $\Delta G = 0$ and $Q = K$.

Spontaneous Reaction at Standard Conditions ($K > 1$)

When the equilibrium constant $K > 1$, the standard Gibbs free energy change $\Delta G^\circ < 0$, making the forward reaction spontaneous under standard conditions.

Nonspontaneous Reaction at Standard Conditions ($K < 1$)

When the equilibrium constant $K < 1$, the standard Gibbs free energy change $\Delta G^\circ > 0$, making the forward reaction nonspontaneous under standard conditions.

Equilibrium at Standard Conditions ($K = 1$)

When the equilibrium constant $K = 1$, the standard Gibbs free energy change $\Delta G^\circ = 0$, indicating that the reaction system is at equilibrium under standard conditions.

Pressure and Volume Shifts in Gas Equilibria

An increase in pressure (or decrease in volume) shifts equilibrium toward the side with fewer moles of gas, whereas a decrease in pressure (or increase in volume) shifts it toward the side with more moles of gas.

Concentration Stress Response

Adding a reactant or removing a product shifts equilibrium forward to form more product, while adding a product or removing a reactant shifts equilibrium backward to form more reactant.

Solid Addition to Chemical Equilibrium

Adding a pure solid reactant or product to an equilibrium reaction mixture causes no shift in the position of equilibrium.

Crystal Lattice

An orderly repeating pattern of molecules in a crystal structure.

Deposition

The direct phase transition from a gas to a solid.

Vaporization

The phase transition from a liquid to a gas.

Melting

The phase transition from a solid to a liquid.