ACE Chemistry

Enthalpy

A state function that measures the total energy or heat content of a system. Abbreviated H. ∆H is positive for endothermic reactions (i.e. absorb heat) and negative for exothermic reactions (i.e. release heat). At constant pressure, ∆H is equivalent to the work done on the system. Cna be defined as the internal energy of a system plus the product of pressure and volume.

Colloid

A type of mixture in which the dispersed particles are smaller than those in a suspension but bigger than those in a solution. A beam of light shown through a colloid is scattered by the Tyndall effect. Specific types include emulsions, foams, gels, and sols. Paint, milk, and smoke are common examples. Stabilize during peptization, which is opposed by flocculation.

Specific heat capacity

Abbreviated C. The amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius. It is defined as one calorie per gram per degree Celsius for water. The Einstein and Debye models describe it, and the Petit-Dulong law explains it through the lattice vibrations of a crystal. For a monatomic ideal gas, it is three halves times the ideal gas constant. It can be approximated as three times Boltzmann's constant times the particle number.

Gibbs free energy

Abbreviated G. THe amount of useful work that can be obtained from a system. It is equal to enthalpy minus the product of temperature and entropy. ∆G=∆H-T∆S. Chemical reactions will only occur spontaneously if ∆G is negative (-). It is minimized when a system reaches equilibrium and at that point is equal to the product of the ideal gas constant, temperature, and the natural log of the equilibrium constant. The molar version is also known as chemical potential. Surface tension is defined as Gibbs free energy divided by surface area. For a redox reaction in a galvanic cell, it is equal to Faraday's constant times the electric potential times the number of moles of electrons.

Lattice energy

Abbreviated U. Measures the strength of ionic bonds in a crystal. It is also the amount of energy needed to separate the molecules in a crystal into an ionic gas. The Born-Lande method and Born-Haber cycle can be used to determine it. Can also be calculated with the Kapustinksii equaion and the Madelung constant.

Kinetic theory of gases

All gas laws make the following assumptions: Gases consist of very small particles in constant, random motion. Except during collisions, molecules exert no forces on each other. The total volume of the individual gas molecules is negligible compared to the volume of the container. Van der Waals' equation tries to correct some of those assumptions for the ideal gas law.

Gold Foil Experiment (or Geiger-Marsden Experiment)

Alpha particles (helium nuclei) fired at a very thin sheet of gold foil. Surrounding sheet of zinc sulfide would light up when struck by an alpha particle. Wide deflection of some particles could only be explained by a dense mass within atoms: the nucleus. The Rutherford (planetary) model of the atom supplanted the Plum Pudding model based on the experiment. Originally sought to prove Plum Pudding Model of atom.

Molecular Orbital (MO) theory

Alternative to VSEPR theory based on regions of electron density called orbitals. Most common molecular orbitals are called sigma and pi. There are bonding and nonbonding (marked with an asterisk) types. Molecular orbitals are determined by the LCAO approximation and are visualized by hybridizations like sp2 and sp3. Mathematically, molecular orbitals are the eigenvalues of the Fock operator in the Hartree-Fock method.

Acids

Arrhenius defined as forming hydrogen ions in water. Bronsted-Lowry definition states that they donate protons. Lewis defined as electron-pair acceptors. Taste sour and feel sticky.

Bases

Arrhenius defined as forming hydroxide ions in water. Bronsted-Lowry definition states that they accept protons. Lewis defined as electron-pair donors. Taste bitter and feel slippery.

Charles' law

At constant pressure, the volume of a gas increases as temperature increases.

Henry's law

At constant temperature, the amount of a gas that will dissolve in a given type and volume of a liquid is directly proportional to the partial pressure of the gas above the liquid. P=k(subscript)HC, P is the partial pressure of the gas, C is the concentration of the gas in solution, and k(subscript)H is a constant. Explains decompression sickness. (AKA the bends).

Boyle's law (Boyle-Mariotte law)

At constant temperature, the pressure and volume of a gas are inversely proportional. Deviations can be modeled by the Joule-Thomson effect. Used to calculate the Carnot cycle. The air pump used to verify it was invented by the namesake scientist's assistant, Robert Hooke.

Gay-Lussac's law (Amonton's law)

At constant volume, the pressure of a gas is directly proportional to its temperature. Main namesake also discovered boron and iodine and made hot-air balloon ascents to study the atmosphere.

Isotope

Atoms with the same atomic number (number of protons) but different mass numbers (different number of neutrons).

Metalloids

B, Si, Ge, As, Sb, Te. Elements whose properties are intermediate between those of metals and non-metals. Used to produce semi-conductors. Many B compounds violate the octet rule. Si is used to make computer chips. As was once considered the "magic bullet" treatment for syphilis and is still the only treatment for many parasitic diseases, like African sleeping sickness.

Alkaline earth metals

Be, Mg, Ca, Sr, Ba, Ra. Silvery, soft metals that form ions with +2 charge. Show a high affinity for water and their salts often form hydrate crystals. Very soluble in ammonia. Epsom salt and gypsum are among their sulfates. Quicklime (CaO) is one of the best known oxides. Mg is found in the chlorophyll molecule. All persons born after 1945 have traces of Sr-90 in their bodies from nuclear weapons. Ba is used as a contrast agent to make the digestive tract visible to X-rays. Ra paints, dyes, and even beverages were once commonly sold because they glowed in the dark.

Atomic orbitals

Can hold only two electrons by the Pauli exclusion principle. Described by the principle, subsidiary, magnetic, and spin quantum numbers. Come in S,P, D, and F types.

Strong bases

Capable of deprotonating very weak acids. All hydroxide of alkali and alkaline earth metals are ones.

London dispersion force

Caused by temporary induced dipoles in molecules. Type of Van der Waals force, which itself is a type of intermolecular force.

Indicator

Chemicals that reversibly change color when exposed to a certain pH. The best known are litmus, a dye extracted from lichens that turns red in acidic conditions and blue in basic conditions, and phenolphthalein, which turns colorless in acids and pink in bases. Used to mark the endpoint of titration. Other common indicators include bromothymol blue, methyl red, Congo red, cresol red, and Genetian violet.

Calorimeter

Device for measuring the heat content of a substance or the heat given off during a reaction. The bomb calorimeter is commonly used in labs. Students often make a simple calorimeter out of Styrofoam cups. Use thermocouples or thermistors as the measuring instrument and have an insulated covering called the jacket.

Allotropes of carbon

Diamond is the hardest known natural mineral. Graphite is the most stable allotrope, found in pencils, lubricants, and arc lamps. A single layer of graphite is called graphene. Fullerenes like buckyballs and nanotubes are at the heart of nanotechnology.

Allotrope

Different structural forms of an element in the same state of matter at room temperature.

Deposition

Direct transition from a gas to a solid. Snow in clouds and frost on windows form by deposition. Chemical-vapor type used to form synthetic diamonds. Easiest method for vitrifying water.

Resonance

Electrons in a molecule delocalize across multiple atoms. Seen in aromatic compounds like benzene. Diagrammed by two or more Lewis dot structures with double-headed arrows connecting them. Although the structures are drawn showing alternating single and double bonds, the actual bonds have an intermediate length, longer than a double bond but shorter than a single bond.

Ionization energy

Energy needed to remove an electron from an atom. Can be first, second, third, etc. depending on the number of electrons removed. Increases across a period from left to right and down a group.

Halogens

F, Cl, Br, I, and At. The only group with elements in all three phases at room temperature. Form diatomic molecules that are extremely reactive and toxic. Form ions with -1 charge. I is used as a mordant in Gram staining and is in Lugol's solution, which turns black in the presence of starch. I is needed by the thyroid to prevent goiter. At is the rarest element on Earth. F is found in Freon and Teflon.

Hydrogen bonds

Form between oxygen, nitrogen, or fluorine of one molecule and hydrogen of another. Result from high electronegativity difference between oxygen, nitrogen, or fluorine and hydrogen. Responsible for all important physical properties of water, like surface tension, capillary action, high heat capacity, use as a universal solvent, and having a less dense solid phase than liquid phase. Responsible for the secondary structure (alpha helix and beta-pleated sheet) of proteins. Also links nucleotides in DNA.

Electrolytes

Free ions that can conduct electricity in solution. Both acids and bases yield electrolytes in water. Described by Ostwald's law of dilution, which includes the constant of protolysis. The Debye-Huckel equation gives their activity coefficient.

Henderson-Hasselbalch equation

Gives the degree to which a compound will deprotonate given its acid dissociation constant and the pH of the solution. Often applied to find the isoelectric point of a protein or a buffer solution.

Clausius-Clapeyron Equation

Gives the slope of a coexistence curve for a phase change in a pressure vs. temperature plot. One version of it is called the Antoine equation. Explains the nonlinear relation between the temperature of a liquid and its vapor pressure. Can be used to model cloud formation.

Deuterium

H-2. Found in heavy water. Often found in solvents for NMR spectroscopy. Almost all was made during Big Bang. Produced in first step of proton-proton chain. Used to slow down enzymes in the primary isotope effect.

Tritium

H-3. Commonly produced by bombarding lithium with neutrons. A small amount is formed when cosmic rays strike atmospheric nitrogen. Used in self-powered beta lights found in watches and exit signs. Necessary for a hydrogen bomb.

Noble gases

He, Ne, Ar, Kr, Xe, Rn. Odorless, colorless, inert gases that do not react with other elements under normal conditions. All have a complete octet of 8 valence electrons, except He, which has a complete valence shell of 2 electrons. Rn is radioactive and is the leading cause of lung cancer among non-smokers. Xenon hexafluoride was the first compound ever created with a noble gas. An alpha particle is a He nucleus. Helium was cooled to form the first superfluid. Give off vibrant colors when charged by an electric current. A tube filled with a noble gas is used to detect ionizing radiation in a Geiger counter.

Hund's rule

If two or more orbitals of a subshell are available then electrons will fill them singly before pairing up. Arises from the fact that more stable atoms have higher spin multiplicity.

Van der Waals forces

Include dipole-dipole interactions and London dispersion forces. Weak forces between atoms or molecules within a substance.

Strong acids

Ionize completely in water. Hydroiodic acid, hydrobromic acid, perchloric acid, hydrochloric acid, and sulfuric acid are the main examples. A mixture of hydrochloric and nitric acids is called "aqua regia" and is capable of dissolving gold.

Plasma

Ionized gas that is considered fourth state of matter. Makes up most of visible mass of universe, including all stars and interstellar medium. On Earth, exists in lightning, polar aurorae, plasma torches, neon lights, and plasma TVs. Transmit Alfven waves and are described by the Vlasov and Saha equation. Can be examined by a Langmuir probe and exhibit Debye interaction length. Named by Langmuir.

Normality

Largely outdated measure of concentration. Equal to molarity divided by an equivalence factor. Still sometimes used to express concentrations of protons or hydroxide ions in an acid or base.

Alkali metals

Li, Na, K, Rb, Cs, and Fr. Dull, soft metals that react violently with water, producing hydroxide ions which give the group its name. Form ions with +1 charge. Rb-87 used to create the first BEC. Cs used in atomic clocks. Li used in batteries and bipolar medication. Cs has the largest atomic radius and Fr is the least electronegative.

pH

Logarithmic scale used to measure the acidity of a solution. Pure water is neutral (pH=7). Acids have pH<7. bases have pH>7. Scale ranges from 0-14.

Catalyst

Lowers the activation energy of a reaction without itself being consumed. Works by introducing an additional transition state and often provides increased surface area for absorption. Biological examples are proteins called enzymes. Can be poisoned if they bind with lead. Many are transition elements like palladium and platinum. Ziegler-Natta ones are made from titanium and are used in polymerization reactions. Chlorofluorocarbons are ones that negatively impact the environment because they speed up the breakdown of ozone in the stratosphere.

Electrolysis

MEthod for breaking apart molecules using an electric current. Famously used to split water into hydrogen and oxygen. Part of anodization (coating metals with a thin layer of another metal), the Hall-Heroult process (extracting aluminum), and the Castner-Kellner process (producing sodium hydroxide). Must overcome thermoneutral voltage to work. By Faraday's law, the mass separated is proportional to the charge passed through. The Fleischmann-Pons experiment that supposedly detected cold fusion involved electrolysis of heavy water using a palladium electrode.

Uranium-235

Main fuel of fission reactors where it splits into barium-141 and krypton-92. Used in "Little Boy" bomb on Hiroshima.

Nernst equation

Major equation of electrochemistry used to find the the potential of a half-cell in a galvanic cell.

Entropy

Measures the disorder of a system. Abbreviated S. It is constantly increasing in the universe by the Second Law of Thermodynamics. Only physical property that can set the direction of the "arrow of time". Can be defined as the Boltzmann constant times the natural log of the number of states of a system. Maxwell's demon reduces it without expending work. Held constant by the Carnot cycle. Can be calculated by the Sackur-Tetrode equation for monatomic ideal gases. For black holes, it is proportional to the event horizon area and inversely proportional to the Planck length squared.

Titration

Method for determining the concentration of unknown solution by adding acid or base of a known concentration. The unknown solution is called the titrand and the known reagent is called the titrant. The titrant is dispensed slowly from a calibrated column called a burette. The endpoint of a titration is often marked by an indicator (e.g. phenolphthalein) changing color. Can be graphed on a titration curve where the inflection points, called equivalence points, mark neutralization. Besides acid-base, there are Fischer, Mohr, zeta potential, and complexometric types.

Distillation

Method for separating components of a liquid mixture by their boiling points. Governed by Raoult's law. There are fractional, steam, and vacuum types. There are apparatuses for the procedure named for Kugelrohr, Perkin, Claisen, and Vigreux. The Fenske equation and McCabe-Thiele method describe the process. The fractional type is used to separate the hydrocarbons in crude oil, but cannot be used on mixtures called azeotropes. An equal mixture of water and ethanol is an azeotrope.

Chromatography

Method for separating mixtures based on the solubility and mass of components. Initially applied to colored dyes and plant pigments, giving the technique its name. Performed by passing a mobile phase through a stationary phase, often in a column. Types include size exclusion, affinity, ion-exchange, thin-layer, high-performance liquid, liquid-gas, gas, and paper types. Each component has a partition coefficient and an R-f value Retardation factor, really an R with a subscript f).

Molality

Moles of solute divided by kilograms of solvent. Method for measuring concentration of a solution.

Molarity

Moles of solute divided by liters of solution. Method for measuring concentration of a solution.

Allotropes of oxygen

Monatomic oxygen is a highly reactive free radical that is rare on Earth but common in the upper atmosphere. DIatomic oxygen is the most common allotrope on Earth. Ozone is a destructive pollutant on Earth but forms a layer of the stratosphere that shields the Earth from UV radiation.

Pauli exclusion principle

No two electrons in an atom can occupy the same quantum state (i.e. possess the same set of quantum numbers). Fermions follow but bosons do not. Explains the electron degeneracy pressure that prevents white dwarfs from collapsing into black holes. Necessitates the color property of quarks. In the liquid drop model, explains the asymmetry energy.

Ideal gas law

PV=nRT. Volume is measured in liters. Temperature is in Kelvin. Pressure is in atmospheres or kPa. n is the number of moles of gas. R is the ideal gas constant. It is a combination of Charles', Boyle's, and Gay-Lussac's laws. It is most accurate at high temperature and low pressure. R is equal to Boltzmann's constant times Avogadro's number. Alternative equations are named for Peng-Robinson and Redlich-Kwong, and deviations can be measured using the virial expansion. Van der Waals' equation is a refinement of the law that includes parameters called a and b, which account for the attraction between molecules and the volume excluded by the molecules, respectively.

Valence Shell Electron Pair Repulsion (VSEPR) theory

Pairs of valence electrons surrounding an atom arrange themselves to be as far apart as possible. Developed by Gillespie and Nyholm. Based on the steric number, or the number of electron pairs around an atom. Must account for both shared pairs (bonds) and lone pairs. Common shapes are linear, bent, trigonal planar, trigonal pyramidal, tetrahedral, trigonal bipyramidal, octahedral, seesaw, T-shaped, and square planar.

Hall-Heroult process

Produces aluminum by electrolysis of a solution of alumina in molten cryolite. Reaction carried out in a Soderberg cell. The alumina is often prepared by the Bayer process, or the dissolution of bauxite ore in sodium hydroxide. The pre-baked version of the process uses solid carbon anodes.

Haber process (Haber-Bosch process)

Produces ammonia by reacting hydrogen and nitrogen. An iron catalyst is used. The hydrogen is derived from syngas (a mixture of hydrogen and carbon monoxide) that is made by heating methane with steam. Ertl received the 2007 Nobel Prize for explaining the catalytic mechanism of the reaction. The process provides most of the fertilizer that sustains the world's population. During World War I, the namesake scientist modified the process to generate saltpeter needed for gunpowder, allowing the Germans to continue the war.

Ostwald process

Produces nitric acid that starts with ammonia and oxygen. Uses a platinum-rhodium catalyst. An intermediate step sees nitrogen dioxide mixed with water.

Solvay process

Produces sodium carbonate (soda ash) from salt brine (NaCl) and limestone (calcium carbonate). Most is used to make glass.

Contact process

Produces sulfuric acid by combining sulfur dioxide and oxygen. Once used a platinum catalyst but now uses a vanadium oxide catalyst. More efficient than the previous lead-chamber process.

Colligative properties

Properties of solutions that only depend on the number of solute particles, not the particle type. Osmotic pressure, freezing point depression, and boiling point elevation are all examples. Calculations require the van't Hoff factor (i).

Amphoteric

Property of a substance to react either as an acid or a base. Water is the most famous example. Commonly used to create buffer solutions. A notable example are zwitterions, which can carry both a positive and negative charge at different locations in the molecule but whose net charge is 0. Amino acids are the most common example.

Redox reaction

Reaction in which one substance is reduced (gains electrons) and another substance is oxidized (loses electrons). In a galvanic cell, oxidation occurs at the anode and reduction occurs at the cathode.

Aufbau principle

Requires electrons to enter atomic orbitals in a pattern that minimizes total potential energy. Basis for assigning electron configurations to elements. Name comes from German word for "building up". Copper and chromium are notable exceptions to the principle. Madelung's rule determines the order of filling and explains the increase in nuclear shielding across a period.

Buffer solutions

Substances that resist changes to their pH. Made from amphoteric substances. Also made from weak acid and its conjugate base. Blood plasma is a common example.

Bose-Einstein Condensate

Supercooled fifth state of matter created in 1995 by Cornell, Wieman, and Ketterle using rubidium-87. Particles collapse into a single quantum mechanical state, effectively forming a "super atom". A recent example is the Tonks-Girardeau gas, and can be analyzed using the Gross-Pitaevskii equation.

Triple point

Temperature and pressure at which a substance exists as a solid, liquid, and gas in equilibrium. For water, defines the Kelvin scale. Gibbs phase rule says a pure substance has no degrees of freedom at the triple point. Any system has p choose three triple points, where p is the number of phases. Helium-4 has two triple points called lambda points because of superfluidity.

Critical point

Temperature and pressure where a phase boundary ceases to exist.

Theoretical yield

The amount of product expected to form from a chemical reaction when all of the reactants are used up. Reduced by side reactions. Can be calculated using mole ratios taken from the balanced equation.

Hess's law of constant heat summation

The change in enthalpy of a reaction is independent of the path from reactants to products. States another way, the total enthalpy change of a reaction can be calculated by summing the enthalpies of each intermediate step. Allows for the calculation of entropy and free energy in the Bordwell cycle and lattice energy in the Haber-Born cycle.

Sublimation

The direct transition from a solid to a gas. Used during lyophilization to freeze-dry perishable materials. Occurs at temperatures and pressures less than the triple point. The enthalpy of sublimation is the sum of the enthalpies of fusion and vaporization. Occurs in dry ice, solid iodine, naphthalene (the main component of moth balls). When done in lab, often followed by "cold finger" for condensing.

Bessemer process

The first widespread mass production method for steel. Air is blown through molten iron to remove sulfur and excess carbon. Apparatus uses openings called tuyeres. A dolomite lining was introduced by Gilchrist-Thomas to solve the "phosphorus problem".

Atomic radius

The mean distance from the nucleus of an atom to the edge of the surrounding electron cloud. Decreases across a period and increases down a group.

Activation energy

The minimum amount of energy needed for a chemical reaction to occur. Can be calculated using the Arrhenius equation.

Avogadro's number

The number of atoms/molecules/anything in a mole, or 6.02x10^23. Equal to Faraday's constant divided by the elementary charge, and the ideal gas constant divided by Boltzmann's constant. Perrin used Brownian motion to calculate it. Define as the number of atoms in 12 grams of carbon-12. Used as the conversion factor between grams and atomic mass units.

Bond order

The number of chemical bonds between a pair of atoms. Double bond=2, triple bond=3, etc. Can be fractional in resonant bonds. Decreases as bond length increases. Easy to calculate in MO theory by subtracting number of antibonding electrons from number of bonding electrons and dividing by two.

Graham's law

The rate at which a gas diffuses/effuses is inversely proportional to the square root of its density. Stated another way, the ratio of the rates of effusion of two gasses is equal to the square root of the inverse ratio of their molar masses. Often used in isotope separation. It was used to determine the formula for ozone. Can be combined with Fick's law to calculate the exchange rates of gases across membranes.

Law of mass action

The rate of a reaction is proportional to the product of the masses or concentrations of the reactants. Can be used to calculate the equilibrium constant by multiplying the product concentrations and then dividing by the reactant concentrations.

Limiting reactant

The reactant used up first in a reaction, limiting the amount of product that actually forms.

Electronegativity

The tendency of an atom to attract shared electrons. Fluorine has highest value on Pauling scale with a 4.0. On the Mulliken scale, it is defined as the average of first ionization energy and electron affinity. Sanderson scale defines it using bond length. Allred-Rochow scale defines it using effective nuclear charge. Can be used to determine the polarity of a bond. Increases from left to right across a period and down a group due to shielding.

Dalton's law of partial pressures

The total pressure of a gaseous mixture is equal to the sum of the partial pressures of the individual components.

Raoult's law

The vapor pressure of a liquid mixture is equal to the sum of each component's partial pressure times its mole fraction. Stated another way, the vapor pressure of a solvent is lowered by the addition of solutes. Is the basis for fractional distillation. Solutions that obey the law are called ideal.

Avogadro's law

Two samples of a gas at the same temperature, pressure, and volume must contain the same number of molecules. Stated another way, one mole of any gas at STP will have a volume of 22.4 L.

Carbon-14

Used in radiocarbon dating of organic samples. Becomes incorporated into organic compounds by photosynthesis. Discovered by Kamen and Ruben. Half-life of 5730 years. Decays into nitrogen-14 through beta decay.

Thermometer

Used to measure temperature. The Beckmann type uses Raoult's law to analyze molar masses of compounds. The Galileo type contains colored glass balls filled with liquids of varying densities. The mercury type was invented by Fahrenheit, who created his temperature scale with 0 degrees as the temperature of a water-ice-ammonium chloride mixture and 100 degrees as normal horse body temperature.

Intermolecular forces

Weak forces responsible for the solubility of substances in polar and non-polar solvents. Examples include Van der Waals forces and hydrogen bonds.

LeChatlier's principle

When the equilibrium of a reversible chemical reaction is changed, the reaction will shift to counteract that change. The equilibrium can be shifted by addition/removal of reactants or products, addition/removal of heat, and changing the pressure (only applicable if at least one substance is a gas). Maintains homeostasis in biological systems. Used in buffer systems. Paul Samuelson applied it to elasticity in economics. Influenced by the common ion effect in which two substances in a chemical reaction can both ionize to give the same ion.

Allotropes of phosphorus

White phosphorus has a tetrahedral arrangement of atoms. Used in weapons because it will ignite spontaneously at low temperatures. Red phosphorus is an amorphous solid used in match tips. Also purple and black allotropes.

Dipole-Dipole interaction

found between molecules with permanent dipoles due to large electronegativity differences. Type of Van der Waals force, which itself is a type of intermolecular force.

Isoelectric point

pH at which a molecule has no net electric charge. Given by the average of the acid dissociation constants of the ionizable groups in a molecule.