General Chemistry II Ch 20, 21 (Exam 3)

Boltzmann equation

The relationship S = k ln W, which connects the entropy of a

system to the number of microstates consistent with its state.

ΔG

The change in Gibbs free energy under the actual conditions of a process

ΔG < 0, ΔG = 0, ΔG > 0

indicates spontaneity, equilibrium, and non spontaneity (respectively)

ΔG°

The standard Gibbs free-energy change for a reaction carried out under

standard-state conditions.

ΔG°f

The standard Gibbs free energy of formation for forming one mole of a

substance from its constituent elements in their stable forms under standard

conditions.

ΔH

The enthalpy change of a process, equal to the heat absorbed by the system

when the process occurs at constant pressure.

ΔH°f

The standard enthalpy of formation for forming one mole of a substance from

its constituent elements in their stable forms under standard conditions.

ΔS

The entropy change of a process, representing the difference between the

entropy of the final and initial states.

Endothermic

A process that absorbs heat from the surroundings into the system

and therefore has ΔH > 0.

Energy dispersal

The spreading of energy among a greater number of particles,

locations, motions, or accessible energy levels, generally increasing the number of

available microstates.

Entropy (S)

A thermodynamic quantity related to the number of microstates

available to a system and the dispersal of energy and matter.

Equilibrium

The condition in which there is no net macroscopic change and ΔG = 0.

Equilibrium constant (K)

The value of the reaction quotient at equilibrium, related to

standard free energy by ΔG° = −RT ln K.

Exothermic

A process that releases heat from the system to the surroundings and

therefore has ΔH < 0.

Gibbs free energy (G)

A thermodynamic quantity defined by G = H − TS that

represents energy available for useful non-expansion work and is used to determine

spontaneity.

Hess’s Law

The enthalpy change for an overall process is the same whether the

process occurs in one step or through a series of steps because enthalpy is a state

function.

Ksp

The solubility-product equilibrium constant that describes the equilibrium

between a sparingly soluble solid and its dissolved ions.

Macrostate

The overall measurable state of a system described by macroscopic

variables such as pressure, volume, temperature, and amount of substance.

Matter dispersal

The spreading of particles over a greater number of possible

locations or arrangements, generally increasing the number of available microstates.

Microstate

One specific way in which the particles and energy of a system can be

distributed while producing the same macroscopic state.

Phase transition

A physical change between states of matter, such as melting or

vaporization, that involves changes in enthalpy and entropy.

Reaction quotient (Q)

A quantity calculated from the current concentrations or

partial pressures of reactants and products that describes the reaction's composition

relative to equilibrium.

Reversible process

A process occurring infinitesimally close to equilibrium whose

direction can be reversed by an infinitesimal change in conditions.

Second Law of Thermodynamics

The entropy of the universe increases during a

spontaneous process and remains unchanged for a process at equilibrium.

Spontaneity

The tendency of a process to undergo a net change without

intervention from outside the system.

Standard state

A defined reference condition in which gases are at 1 atm, aqueous

species are at 1 M, elements are in their stable forms, and temperature is specified.

State function

A property whose value depends only on the current state of a

system, so its change depends only on the initial and final states and not on the path

taken.

Surroundings

Everything outside the system that can exchange energy with the

system.

S° (standard entropy)

The absolute entropy of a substance in its standard state at a

specified temperature, typically tabulated at 25.0°C.

System

The specific portion of the universe being studied in a thermodynamic

analysis.

Thermodynamics

The study of energy, heat, work, and the conditions that

determine whether physical and chemical processes can occur spontaneously.

Third Law of Thermodynamics

A perfect crystal has zero entropy at absolute zero,

0 K.

Trouton’s Rule

The empirical observation that the entropy of vaporization for many

substances at their normal boiling points is approximately 85 J·K−1·mol−1.

Universe

In thermodynamics, the combination of the system and its surroundings.

ampere (A)

The SI unit of electric current; 1 ampere of current results when 1 coulomb of charge flows through a conductor in 1 second.

anode

The electrode at which oxidation occurs in an electrochemical cell. Electrons are given up by the reducing agent and leave the cell at the anode.

battery

A group of voltaic cells arranged in series; primary and secondary types are self-contained, but flow batteries are not.

cathode

The electrode at which reduction occurs in an electrochemical cell. Electrons enter the cell and are acquired by the oxidizing agent at the cathode.

cell potential (Ecell)

(also electromotive force,or emf; cell voltage) The difference in electrical potential between the two electrodes of an electrochemical cell.

concentration cell

A voltaic cell in which both compartments contain the same components but at different concentrations.

corrosion

The natural redox process that results in unwanted oxidation of a metal.

coulomb (C)

The SI unit of electric charge. One coulomb is the charge of 6.242 × 10¹⁸ electrons; one electron possesses a charge of 1.602 × 10⁻¹⁹ C.

electrochemical cell

A system that incorporates a redox reaction to produce or use electrical energy.

electrochemistry

The study of the relationship between chemical change and electrical work.

electrode

A solid surface in an electrochemical cell that conducts electrons into or out of each half-cell.

electrolysis

The nonspontaneous lysing (splitting) of a substance, often to its component elements, by the input of electrical energy.

electrolyte

A mixture of ions, in which the electrodes of an electrochemical cell are immersed, that conducts a current.

electrolytic cell

An electrochemical system that uses electrical energy to drive a nonspontaneous chemical reaction
(ΔG> 0).

electromotive force (emf)

The difference in electrical potential between the two electrodes of an electrochemical cell.

Faraday constant (F)

The physical constant representing the charge of 1 mol of electrons:F= 96,485 C/mol e⁻.

fuel cell

(also flow battery) A battery that is not self-contained and in which electricity is generated by the controlled oxidation of a fuel.

half-cell

A portion of an electrochemical cell in which a half-reaction takes place.

half reaction method

A method of balancing redox reactions by treating the oxidation and reduction half-reactions separately.

Nernst equation

An equation stating that the voltage of an electrochemical cell under any conditions depends on the standard cell voltage and the concentrations of the cell components: Ecell = Eºcell - (RT)/(nF) • lnQ

overvoltage

The additional voltage, usually associated with gaseous products forming at an electrode, that is required above the standard cell voltage to accomplish electrolysis.

salt bridge

An inverted U tube containing a solution of nonreacting ions that connects the compartments of a voltaic cell and maintains neutrality by allowing ions to flow between compartments.

standard cell potential (Eºcell)

The potential of a cell measured with all components in their standard states and no current flowing.

standard electrode (half-cell) potential (Eºhalf-cell)

(also standard half-cell potential) The standard potential of a half-cell, with the half-reaction written as a reduction.

standard hydrogen electrode (SHE)

A specially prepared platinum electrode immersed in 1MH⁺(aq) through which H₂ gas at 1 atm is bubbled. Eºhalf cell is defined as 0 V.

volt (V)

The SI unit of electrical potential: 1 V = 1 J/C.

voltage

The difference in electrical potential between the two electrodes of an electrochemical cell.

voltaic (galvanic) cell

(also galvanic cell) An electrochemical cell that uses a spontaneous redox reaction to generate electrical energy.