unit 3

Chemical Equilibrium

A state reached by all reversible reactions where the amounts of reactants and products are no longer changing because the forward and backward rates are equal.

Equilibrium Constant (K)

A characteristic ratio of products to reactants at equilibrium, defining the relationship between the concentrations of reactants and products.

Reaction Quotient (Q)

A ratio of products to reactants at any point in time during a reaction, which can be used to predict the direction of change towards equilibrium.

Le Chatelier’s Principle

An equilibrium system subjected to stress will shift in the direction that relieves the stress.

Q > K

Indicates there are too many products, prompting the equilibrium to shift toward reactants.

Q < K

Indicates there are too many reactants, prompting the equilibrium to shift toward products.

Calculating Q

Involves using concentrations of products raised to their coefficients divided by concentrations of reactants raised to their coefficients.

Stress on Equilibrium

Alterations in concentration, temperature, or volume that impact the position of equilibrium.

K and Temperature Change

K changes with temperature; for endothermic reactions (ΔH > 0) heat is treated as a reactant, and for exothermic reactions (ΔH < 0) heat is treated as a product.

No Solids or Liquids in Q

The addition or removal of solids or pure liquids does not affect the reaction quotient, only aqueous and gaseous species are included.

Equilibrium Constant (K)

A numerical value that represents the ratio of the concentration of the products to the concentration of the reactants at equilibrium.

Solubility Product Constant (Ksp)

The equilibrium constant for the solubility of a sparingly soluble ionic compound expressed as the product of the concentrations of its ions.

Le Chatelier's Principle

If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change.

Common Ion Effect

The reduction in solubility of an ionic compound when a common ion is added to the solution.

Saturated Solution

A solution that has reached the maximum concentration of solute that can be dissolved at a given temperature and pressure.

Dissolution Equilibrium

The state in which the rate of dissolution of a solid into a solution equals the rate of precipitation of that solid from the solution.

Molarity (M)

A measure of concentration representing the number of moles of solute per liter of solution.

Concentration Quota (Q)

The ratio of the concentrations of products to reactants at a given time, which can help predict the direction of the shift in equilibrium.

Equilibrium Shift

The change in the concentrations of reactants and products to reach a new equilibrium state when disturbed.

Solubility Limit

The maximum concentration of a solute that can dissolve in a solvent at a given temperature and pressure.

Endergonic Reaction

A reaction that is nonspontaneous and favors reactants, indicated by a positive ΔG.

Exergonic Reaction

A reaction that is spontaneous and favors products, indicated by a negative ΔG.

Chemical Equilibrium

A state reached by reversible reactions where the amounts of reactants and products remain constant over time.

Equilibrium Constant (K)

A ratio that expresses the concentrations of products and reactants at equilibrium; often regarded as unitless.

Reversible Reaction

A reaction that can proceed in both the forward and backward directions, represented as A ⇌ B.

Limiting Reactant

The reactant that is completely consumed in a reaction, determining the extent of the reaction.

Spontaneous Reaction

A reaction that occurs without needing to be driven by an external force, generally favoring products.

Forward Rate vs Backward Rate

The rates of the reaction in the forward and reverse directions, which become equal at equilibrium.

Molarity (M)

A concentration unit defined as moles of solute per liter of solution, used for aqueous and gas states.

Partial Pressure

The pressure exerted by a single component of a gas mixture, used in equilibrium calculations for gases.

Equilibrium Constant (K)

A value that expresses the ratio of the concentration of products to reactants at equilibrium.

Dissociation

The process in which a compound breaks down into smaller components, often into ions, when dissolved in water.

Acid

A substance that donates protons (H+) in water or forms hydronium ions (H3O+).

Base

A substance that produces hydroxide ions (OH–) in water.

Neutral

A solution that has equal concentrations of H+ and OH–, resulting in a pH of 7.

Strong Acid

An acid that completely dissociates in solution, producing a large concentration of H3O+.

Weak Acid

An acid that partially dissociates in solution, producing a small concentration of H3O+.

Acid Strength (Ka)

The equilibrium constant for the dissociation of an acid, indicating how well it donates protons.

Base Strength (Kb)

The equilibrium constant for the dissociation of a base, indicating how well it produces hydroxide ions.

pH

The negative logarithm of the hydrogen ion concentration, used to measure the acidity or basicity of a solution.

Water Dissociation

The process where water dissociates into hydronium (H3O+) and hydroxide (OH–) ions.

Hydronium Ion (H3O+)

A positively charged ion formed when a water molecule gains a proton.

Hydroxide Ion (OH–)

A negatively charged ion formed when a water molecule loses a proton.

Reaction of Acids and Bases

When an acid reacts with a base, they neutralize each other, producing water and a salt.

Equilibrium Expression (K)

Represents the ratio of concentrations of products to reactants at equilibrium.

Ka

Acid dissociation constant, quantifies the strength of an acid in solution.

Kb

Base dissociation constant, quantifies the strength of a base in solution.

pH

Measure of acidity or alkalinity of a solution, calculated as -log[H+].

Neutralization

Reaction where an acid and a base react to form water and a salt.

Strong Acid

Acid that completely dissociates in solution, like HCl.

Weak Acid

Acid that does not completely dissociate in solution, like acetic acid (CH3COOH).

Limiting Reactant

The substance that is completely consumed in a reaction, determining the amount of product formed.

pOH

Measure of the hydroxide ion concentration, calculated as -log[OH-].

Inversely Related

Referring to how [H+] and [OH-] concentrations change in relation to one another; as one increases, the other decreases.

Equimolar reaction

Acid-base reaction where equal moles of acid and base produce neutral water.

Strong Acid

An acid that completely dissociates in solution, characterized by large $K_a$ values.

Weak Acid

An acid that partially dissociates in solution, characterized by small $K_a$ values.

Strong Base

A base that completely dissociates in solution, characterized by large $K_b$ values.

Weak Base

A base that partially dissociates in solution, characterized by small $K_b$ values.

Conjugate Acid

The species formed when a base gains a proton.

Conjugate Base

The species formed when an acid loses a proton.

pH Scale

A logarithmic scale used to specify the acidity or basicity of an aqueous solution.

Neutralization Reaction

A reaction between an acid and a base that produces water and a salt.

RICE Table

A tool used to calculate the concentrations of reactants and products at equilibrium after a reaction.

pKa

The negative logarithm of the acid dissociation constant (Ka), indicating acid strength.

pKb

The negative logarithm of the base dissociation constant (Kb), indicating base strength.

Unequal moles

In a reaction, when the moles of acid and base are not equal, resulting in excess reactants.

Ka x Kb = Kw

Relationship indicating the product of an acid's dissociation constant and its conjugate base's dissociation constant equals the ion product of water.

Ka (acid dissociation constant)

A quantitative measure of the strength of an acid in solution.

Kb (base dissociation constant)

A quantitative measure of the strength of a base in solution.

Equilibrium Reaction

A reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction.

Strong Acid Example

HCl, which dissociates completely in solution.

Weak Acid Example

Acetic acid (CH3COOH), which only partially dissociates.

Salt Formation

The product of a neutralization reaction, comprising the cation from the base and the anion from the acid.

CH3COOH

Acetic acid, a weak acid used in the warm-up calculations.

NaOH

Sodium hydroxide, a strong base used to neutralize the acetic acid.

RICE table

A table used to determine the concentrations of reactants and products at equilibrium.

pH

A measure of how acidic or basic a solution is.

Equivalence point

The point in a titration at which the amount of titrant is stoichiometrically equivalent to the amount of analyte.

Weak base

A substance that partially ionizes in solution and produces hydroxide ions.

Epinephrine

A weak base with pKb = 5.4 used in the titration example.

Limiting reactant

The reactant that is completely consumed in a reaction, limiting the amount of products formed.

HCOOH

Formic acid, another weak acid used in titration examples.

Molarity

A way to express the concentration of a solution; moles of solute per liter of solution.

Titration

The process of adding a solution of known concentration to determine the concentration of an unknown solution.

pKa

The negative logarithm of the acid dissociation constant (Ka); indicates the strength of an acid.

pKb

The negative logarithm of the base dissociation constant (Kb); indicates the strength of a base.

Stronger reactant

A reactant that completely dissociates or ionizes in solution, often affecting pH.

Excess acid

Condition in a titration where the acid is present in greater quantity than needed to neutralize the base.

Buffer Solution

A solution containing large amounts of both a weak acid and its conjugate base that resists large changes in pH upon the addition of strong acid or base.

Equivalence Point

The point in titration where the amount of titrant added exactly neutralizes the analyte solution.

Half-Equivalence Point

The point in titration where half of the analyte has been neutralized; pH is equal to pKa of the acid.

pKb

The negative logarithm of the base dissociation constant (Kb); low pKb means a stronger base.

RICE Table

A table used to calculate the concentrations of reactants and products at equilibrium; stands for Reaction, Initial, Change, Equilibrium.

Titration Curve

A graph that depicts the pH change of a solution as a function of the volume of titrant added.

pH at Half-Equivalence Point

Equal to the pKa of the weak acid being titrated.

Acetic Acid

A weak acid commonly used in buffer solutions, with the formula CH3COOH.

Conjugate Base

The species that remains after an acid donates a proton.

Strong Acid

An acid that completely dissociates in solution, leading to a high concentration of H+ ions.

Weak Acid

An acid that partially dissociates in solution, resulting in equilibrium between the acid and its ions.