Chemistry 40s - Exam Definitions

Electrochemical Cell

An apparatus that uses a redox reaction to produce electrical energy or uses electrical energy to cause a chemical reaction.

Salt Bridge

A pathway constructed to allow positive and negative ions to move from one solution to another.

Voltaic Cell

A type of electrochemical cell that converts chemical energy into electrical energy by a spontaneous redox reaction

Anode

In an electrochemical cell, the electrode where oxidation takes place.

Cathode

In an electrochemical cell, the electrode where reduction takes place

Reduction Potential

The tendency of a substance to gain electrons

Battery

One or more electrochemical cells in a single package that generates electrical current.

Dry Cell

An electrochemical cell that contains a moist electrolytic paste inside a zinc shell.

Primary Batteries

A type of battery that produces electric energy by redox reactions that are not easily reversed, delivers current until the reactants are gone, and then is discarded.

Secondary Batteries

A rechargeable battery that depends on reversible redox reactions.

Corrosion

The loss of metal that results from an oxidation-reduction reaction of the metal with substances in the environment

Electrolysis

The process that uses electrical energy to bring about a chemical reaction

Electrolytic Cell

An electrochemical cell in which electrolysis occurs

Galvanizing

The process in which an iron object is dipped into molten zinc or electroplated with zinc to make the iron more resistant to corrosion.

Redox Reactions

An oxidation-reduction reaction.

Oxidation

The loss of electrons from the atoms of a substance; increases an atom’s oxidation number.

Reduction

The gain of electrons by the atoms of a substance; decreases an atom’s oxidation number.

Oxidizing Agent

The substance that oxidizes another substance by accepting its electrons.

Reducing Agent

The substance that reduces another substance by losing electrons.

Oxidation-number Method

the technique that can be used to balance more difficult redox reactions, based on the fact that the number of electrons transferred from atoms must equal the number of electrons accepted by other atoms.

Species

Any kind of chemical unit involved in a process.

Half Reaction

One of two parts of a redox reaction — the oxidation half, which shows the number of electrons lost when a species is oxidized, or the reduction half, which shows the number of electrons gained when a species is reduced.

Electrochemical Processes

The conversion of chemical energy into electrical energy and the conversion of electrical energy into chemical energy are known as these processes.

Hydrochloric Acid

HCl

Nitric Acid

HNO3

Sulfuric acid

H2SO4

Phosphoric Acid

H3PO4

Acetic Acid

HC2H3O2

Carbonic Acid

H2CO3

Potassium Hydroxide

KOH

Sodium Hydroxide

NaOH

Calcium Hydroxide

Ca(OH)2

Arrhenius Acid

Acids are compounds containing hydrogen that ionize to yield hydrogen ions (H+) in aqueous solution.

Arrhenius Base

Bases are compounds that ionize to yield hydroxide ions (OH-) in aqueous solution.

Monoprotic Acid

Contain one ionizable hydrogen.

Diprotic Acid

Contain two ionizable hydrogen.

Triprotic Acid

Contain three ionizable hydrogen.

Bronsted-Lowry Acid

A model of acids and bases in which an acid is a hydrogen-ion donor and a base is a hydrogen-ion acceptor.

Bronsted-Lowry Base

A hydrogen ion acceptor.

Conjugate Base

The species produced when an acid donates a hydrogen ion to a base.

Conjugate Acid

The species produced when a base accepts a hydrogen ion from an acid.

Self-Ionization of water

The reaction in which two water molecules react to give ions.

Titration

The process in which an acid-base neutralization reaction is used to determine the concentration of a solution of unknown concentration.

Standard solution

A solution of known concentration used in carrying out a titration.

Endpoint

The point at which the indicator that is used in a titration changes color.

Equivalence point

The point at which the moles of H+ ions from the acid equals moles of OH- ions from the base.

Buffer

A solution that resists changes in pH when limited amounts of acid or base are added.

Buffer Capacity

The amount of an acid or base a buffer solution can absorb without a significant change in pH.

Titrant

A solution of known concentration used to titrate a solution of unknown concentration; also called the standard solution.

Buret

A buret is a precisely marked glass cylinder. It measures the volumes of reacting solutions.

Physical Equilibrium

Occurs when there is no net change in a physical system and no new substances are formed.

Reversible Reaction

A reaction that can take place in both the forward and reverse directions; leads to an equilibrium state where the forward and reverse reactions occur at equal rates and the concentrations of reactants and products remain constant.

Chemical Equilibrium

The state in which forward and reverse reactions balance each other because they occur at equal rates.

Closed System

A system where only the exchange of energy occurs but the exchange of matter is not.

Le Chatelier's Principle

States that if a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress.

Heterogeneous Equilibrium

A state of equilibrium that occurs when the reactants and products of a reaction are present in more than one physical state.

Common Ion Effect

The lowering of the solubility of a substance by the presence of a common ion.

Homogeneous Equilibrium

A state of equilibrium that occurs when all the reactants and products of a reaction are in the same physical state

Law of Chemical Equilibrium

States that at a given temperature, a chemical system may reach a state in which a particular ratio of reactant and product concentrations has a constant value.

Solubility Product Constant

Ksp, which is an equilibrium constant for the dissolving of a sparingly soluble ionic compound in water

Precipitate

A solid produced during a chemical reaction in a solution

Dynamic Equilibrium

Occurs in reversible reactions where products and reactants are formed at such a rate that neither of their concentrations change.

Equilibrium Constant

Keq, is the numerical value that describes the ratio of product concentrations to reactant concentrations, with each raised to the power corresponding to its coefficient in the balanced equation.

Reaction Rate

The change in concentration of a reactant or product per unit time, generally calculated and expressed in moles per liter per second.

Collision Theory

States that atoms, ions, and molecules must collide in order to react.

Activation Energy

The minimum amount of energy required by reacting particles in order to form the activated complex and lead to a reaction.

Activated Complex

A short-lived, unstable arrangement of atoms that can break apart and re-form the reactants or can form products; also sometimes referred to as the transition state.

Homogeneous Catalyst

A catalyst that exists in the same physical state as the reaction it catalyzes.

Heterogeneous Catalyst

A catalyst that exists in a different physical state than the reaction it catalyzes.

Reaction Order

For a reactant, describes how the rate is affected by the concentration of that reactant.

Complex Reaction

A chemical reaction that consists of two or more elementary steps.

Instantaneous Rate

The slope of the straight line tangent to the curve at a specific time

Reaction Mechanism

The complete sequence of elementary steps that make up a complex reaction.

Intermediate

A substance produced in one elementary step of a complex reaction and consumed in a subsequent elementary step.

Rate-Determining Step

The slowest elementary step in a complex reaction; limits the instantaneous rate of the overall reaction.

Inhibitor

A substance that slows down the reaction rate of a chemical reaction or prevents a reaction from happening.