Chemical Equilibrium and Acid-Base Chemistry

Flashcards covering the definitions and concepts of chemical equilibrium, Le Châtelier’s Principle, and acid-base chemistry based on lecture notes.

Chemical Equilibrium

A state reached when the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant.

Physical Equilibrium

An equilibrium established between different phases of the same substance, such as $H_2O (l) \rightleftharpoons H_2O (g)$.

Equilibrium Constant ($K_{eq}$)

A unitless value representing the ratio of products to reactants, including reaction coefficients, used to describe the extent of a reaction.

Law of Mass Action

A rule stating that the equilibrium constant is the ratio of products to reactants, each raised to the power of its coefficient in the balanced equation.

Homogeneous Equilibrium

Refers to reactions in which all reactants and products are in the same physical phase.

Heterogeneous Equilibrium

Refers to reactions in which reactants and products are in different physical states, such as solids and gases.

$$K_p$$

The equilibrium constant for gas-phase reactions expressed in terms of partial pressures, related to $Kc$ by $K_p = K_c(RT)^{\Delta n}$.

$$\Delta n$$

The difference between the number of moles of gaseous products and the number of moles of gaseous reactants.

Reaction Quotient ($Q_c$)

The ratio of products to reactants at any given time point, calculated using the same expression as $K_c$ to determine the direction a reaction will shift to reach equilibrium.

Le Châtelier’s Principle

The principle stating that if an external stress (change in concentration, volume, pressure, or temperature) is applied to a system at equilibrium, the system adjusts to partially offset the stress.

Catalyst

A substance that lowers the activation energy ($E_a$) for both forward and reverse reactions, allowing equilibrium to be reached sooner without shifting the equilibrium position or changing $K$.

Bronsted Acid

A substance able to donate a proton ($H^+$) to another substance.

Bronsted Base

A substance able to accept a proton ($H^+$), typically containing $-OH$ or $N$.

Arrhenius Acid

A substance that produces $H^+$ ($H_3O^+$) when dissolved in water.

Lewis Acid

A substance that can accept a pair of electrons.

Lewis Base

A substance that can donate a pair of electrons.

Conjugate Base

The base that is produced when a Bronsted acid donates its proton.

Conjugate Acid

The acid that is produced when a Bronsted base accepts a proton.

pH

A logarithmic scale reflecting the concentration of $H^+$ in solution, calculated as $pH = -\log [H^+]$.

Ion-product constant ($K_w$)

The equilibrium constant for the auto-ionization of water, which is $1.0 \times 10^{-14}$ at $25^\circ\text{C}$.

Strong Electrolyte

A substance that undergoes $100\%$ dissociation in solution, such as strong acids like $HCl$.

Acid Dissociation Constant ($K_a$)

The equilibrium constant for the ionization of a weak acid, representing its strength.

Percent Ionization

The ratio of the ionized acid concentration at equilibrium to the initial acid concentration, multiplied by $100\%$.

Oxoacid

An acid containing one or more $-OH$ groups and oxygen atoms bound to a central non-metal atom.

Diprotic Acid

An acid that can donate two protons, losing them one at a time with a separate $K_a$ for each step.

Amphoteric Molecule

A molecule, such as the conjugate base of a diprotic acid, that can function as both an acid and a base.