General Chemistry

Triple Point

A point on a phase diagram at which a substance exists in equilibrium between all three phases.

System

The part of the universe under consideration that is separated by some real or imaginary boundary from its surroundings.

State Function

A variable that depends only on the current state of a system, and not the path taken to get there. Includes pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, and entropy.

Spontaneous Reaction

A reaction that will proceed or occur on its own without additional energy input from its surroundings.

Process Function

A variable that depends on the path taken to get from one state to another. Includes work and heat.

Phase Diagram

A pressure-temperature plot showing the conditions under which a substance exists in pure phase or in equilibrium between different phases.

Open System

A system that allows for the exchange of energy and matter across its boundaries.

Law of Conservation of Energy

Law stating that energy cannot be created or destroyed but only transferred and transformed.

Isovolumetric (Isochoric) Process

A process in which volume remains constant and no net pressure-volume work is done.

Isothermal Process

A process in which temperature (and, therefore, internal energy) remains constant.

Isolated System

A system that can exchange neither energy nor matter with its surroundings.

Isobaric Process

A process that occurs at a constant pressure

Hess's Law

States that the enthalpy change of an overall reaction is equal to the sum of the standard heats of formation of the products minus the sum of the standard heats of formation of the reactants.

Exothermic

A reaction that proceeds with the net release of heat into the surroundings.

Endothermic Reaction

A reaction that proceeds with the net absorption of heat from the surroundings.

Constant-Volume Calorimeter

An apparatus commonly referred to as a bomb calorimeter; used to measure the amount of heat absorbed or released during a reaction.

Closed System

A system that allows for the exchange of energy, but not matter, across its boundaries.

Adiabatic Process

A process in which no heat is transferred to or from the system by its surroundings.

Specific Heat

The amount of heat required to raise one gram of a substance by one degree Celsius.

Heat

A transfer of energy from a substance with a higher temperature to a substance with a lower temperature.

Gibbs Free Energy

The energy of a system available to do work.

Entropy

The chaos or randomness of a system, often denoted by *S*. Δ*S* represents the change in entropy following a reaction.

Enthalpy

The total heat content of a system at a constant pressure, commonly denoted by *H*.

Transition Elements

The elements found in the B groups of the Periodic Table. These elements contain partially filled *d* subshells.

Noble Gas

Inert elements naturally existing in a gaseous state that comprise Group VIII (Group 18) of the Periodic Table.

Halogens

Elements found in Group VIIA (Group 17) of the Periodic Table.

Effective Nuclear Charge

The resulting positive nuclear charge an outer electron senses after accounting for the shielding effect of inner core electrons. Abbreviated *Z*_eff. Increases from left to right and from bottom to top on the Periodic Table.

Alkaline Earth Metals

Elements found in Group IIA (Group 2) of the Periodic Table.

Alkali Metals

The highly reactive elements found in Group IA (Group 1) of the Periodic Table, except hydrogen.

Nonmetals

Elements that have characteristically high electronegativity, ionization energy, and electron affinity. These elements tend to be found on the right side of the Periodic Table and are poor conductors of electricity

Metalloids

Elements that have properties between those of metals and nonmetals; includes B, Si, Ge, As, Sb, Te, Po, and At.

Ionization Energy

The amount of energy required to remove an electron from orbit about a gaseous atom into free space. Increases from left to right and from bottom to top on the Periodic Table.

Electronegativity

A measure of an atom's ability to pull electron density toward itself when involved in a chemical bond. Increases from left to right and from bottom to top on the Periodic Table.

Electron Affinity

The energy released when an atom or ion in the gaseous state gains an electron. Increases from left to right and from bottom to top on the Periodic Table.

Standard Temperature and Pressure (STP)

273 Kelvin (0° Celsius) and 1 atmosphere (760 mmHg).

Partial Pressure

The pressure contribution of a single gas in a container holding a mixture of gases, as given by: *P*ₐ = *X*ₐ *P*ₜₒₜₐₗ, where *X*ₐ is the mole fraction of gas A and *P*ₜₒₜₐₗ is the total pressure of the mixture.

Kinetic Molecular Theory of Gases

A series of assumptions used to account for the behavior of ideal gases. The theory describes gases as volumeless particles in constant, random motion that exhibit no intermolecular attractions and undergo completely elastic collisions with each other and the walls of their container.

Ideal Gas

A hypothetical gas containing particles with zero volume and with no attractive intermolecular forces

Henry's Law

States that the partial pressure of a gas dissolved in a solution is directly proportional to the partial pressure of this gas above the solution.

Graham's Law

Law stating that the rates at which two different gases effuse or diffuse are inversely proportional to the square root of their molar masses: r1/r2=√M2/M1

Gay-Lussac's Law

States that at a constant volume, the pressure of an ideal gas is directly proportional to its temperature.

Charles's Law

States that at a constant pressure, the volume of an ideal gas is directly proportional to its temperature.

Boyle's Law

at a constant temperature, the volume of gas is inversely proportional to its pressure.

Avogadro's Principle

States that the number of moles of a gas present is proportional to its volume, assuming constant pressure and temperature.

Ideal Gas Law

*PV* = *nRT*.

Effusion

movement of gas from one compartment to another through a small opening under pressure.

Diffusion

Passive dispersion of a gas or solute throughout a medium by means of random motion.

Solvent

A medium, commonly a liquid, into which a solute is dissolved to create a solution.

Solvation

The process of forming a cagelike network of solvent molecules around a solute in a solution.

Solution Equilibrium

When a solute is dissolved in a solvent, it will dissociate until reaching an equilibrium point at which the rate of dissociation equals the rate of precipitation of the solute, regardless of any additional solute introduced into the mixture.

Solute

A compound, commonly an ion, dissolved in a solvent to create a solution.

Solubility Product Constant

The product of the molar concentrations of dissociated ions in a saturated solution, where each ion is raised to the power of its stoichiometric coefficient. Denoted *K*ₛₚ.

Solubility

A ratio that measures how much solute can dissolve in a solvent at a given temperature.

Raoult's Law

States that the vapor pressure of a solvent is proportional to the mole fraction of the solvent in the solution; provides an explanation for the boiling point elevation seen in solutions.

Molarity

Concentration of a solution calculated by moles of solute per liters of solution, often denoted by *M*

Molality

Concentration of a solution calculated by moles of solute per kilograms of solvent, often denoted by *m*

Ion Product

The product of the molar concentrations of dissociated ions in solution at any point in a dissociation reaction, where each ion is raised to the power of its stoichiometric coefficient. Denoted *IP*.

Aqueous Solution

A solution containing water as its solvent

pH

Scaled value used to measure the acidic strength of a solution, calculated by taking the negative logarithm of the proton concentration in a solution: pH = -log \[H⁺\].

Molar Solubility

The molarity of a solute such that a solution is saturated (at equilibrium).

Concentration

The ratio of the amount of solute to the amount of solution; quantified by mole fraction, molarity, molality, or normality, among other measures.

Common Ion Effect

States that the molar solubility of one salt is reduced when another salt, having a common ion, is brought into the same solution.

Colligative Properties

The properties of solutions—such as vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure—that are affected only by the number of solute particles dissolved and not by their chemical identities.

Reducing Agent

A species that is oxidized in the process of reducing another species.

Oxidizing Agent

A species that is reduced in the process of oxidizing another species.

Oxidation-Reduction Half-Reaction

A hypothetical equation showing only the species that is oxidized or reduced in a oxidation-reduction reaction and the correct number of electrons transferred between the species in the complete, balanced equation.

Net Ionic Equation

A representation of a displacement reaction showing only the reactive species and omitting the spectator ions.

Free Radical

An atom or molecule that has an unpaired electron in its outermost shell.

Disproportionation (Dismutation)

An oxidation-reduction reaction in which the same species is both oxidized and reduced.

Reduction

A reaction in which a species gains electrons.

Oxidation

A reaction in which a species loses electrons

Reversible Reaction

A process that will proceed bidirectionally to form both product and reactant.

Le Châtelier's Principle

States that when a system in equilibrium is placed under one of several stressors, it will react in order to regain equilibrium.

Reaction Quotient

The ratio of the concentrations of the products to the concentrations of the reactants at any point during a reaction, where each reactant and product in the expression is raised to the power of its stoichiometric coefficient. Commonly denoted by *Q*. Usually compared to the equilibrium constant to determine the direction a reaction will proceed to regain equilibrium.

Equilibrium

A dynamic point reached by a reversible reaction in which the rate of the forward reaction is equal to the rate of the reverse reaction. There is no net change in the concentrations of the products and reactants over time.

Reduction Potential

A measure of the tendency of a species to be reduced, commonly used in identifying the anode and cathode of an electrochemical cell.

Nernst Equation

An equation used to determine a cell's electromotive force (emf) when conditions are not standard. Ecell=E^0cell−0.0592/n logQ  where *E*_cell is the emf,  E^ocell is the emf under standard conditions, *n* is the number of electrons transferred in the oxidation-reduction reaction, and *Q* is the reaction quotient.

Half-Cell

An electrode immersed in an electrolytic solution that is the site of either oxidation or reduction in an electrochemical cell.

Galvanic Cell

An electrochemical cell powered by a spontaneous oxidation-reduction reaction that produces an electric current; also called a voltaic cell.

Faraday's Constant

Denoted by F, it equals  9.65 × 104 Cmol e Commonly used in the formula *It* = *n*F, where *I* is current, *t* is time (in seconds), and *n* is moles of electrons transferred.

Electrolytic Cell

/ An electrochemical cell that uses an external electric source to drive a nonspontaneous (unfavorable) oxidation-reduction reaction.

Electrochemical Reaction

A chemical reaction that either is driven by or produces electricity.

Cathode

/ The electrode at which reduction occurs during a cell's oxidation-reduction reaction. Electrons always flow toward the cathode in an electrochemical cell.

Anode

/ The electrode where oxidation occurs during a cell's oxidation-reduction reaction. Electrons always flow from the anode in an electrochemical cell.

Equilibrium Constant

/ The ratio of the concentrations of the products to the concentrations of the reactants at the point of equilibrium, where each reactant and product in the expression is raised to the power of its stoichiometric coefficient. Commonly denoted by K_eq.

Single-Displacement Reaction

/ A chemical reaction in which an atom or ion of one compound is replaced by another atom or ion (such as A + BC → B + AC).

Limiting Reagent

/ The reactant in a chemical equation that, given nonstoichiometric amounts, determines the amount of product that can form; the reactant that runs out first.

Empirical Formula

/ Chemical formula showing the smallest whole-number ratio of atoms in a compound.

Electrolyte

/ An ion in water that is capable of conducting electricity in that solution.

Double-Displacement Reaction

/ A chemical reaction in which two different compounds exchange an atom or ion to form two new compounds (such as AB + CD → AD + CB); also called a metathesis reaction.

Decomposition Reaction.

/ A chemical reaction in which one substance breaks down into two substances (such as A → B + C)

Combination Reaction

/ A reaction in which two or more reactants combine to form a product (such as A + B → C).

Theoretical Yield

/ The expected amount of product yielded in a reaction according to the reactants' stoichiometry.

Percent Yield

/ A ratio (calculated as a percentage) of the actual mass of product yielded to the theoretical yield of product mass.

Percent Composition

/ The percentages of the elements making up a compound (usually by mass in amu).

Molar Mass

/ The sum of all the masses present (in amu) in one molecule of a molecular compound.

Reaction Rate

/ The measure of how quickly reactants are consumed and products are formed, commonly expressed in terms of mol L⁻¹ s⁻¹.

Reaction Order

/ The sum of the exponents in a rate law, where each exponent provides the reaction order with respect to its reactant.

Reaction Mechanism

/ A "play-by-play" showing the individual steps of a reaction, including the formation and destruction of any reaction intermediates that may occur.

Rate Law

/ An experimentally determined mathematical expression showing the rate of a reaction as a function of the concentrations of its reactants.