Student Resources
Definitions

Acid

Any substance that can act as a proton (H+ ion) donor, in the Bronsted-Lowry model of acids and bases.

acid ionization constant The equilibrium constant, given the symbol Ka, for the reaction of an acid with water resulting in the production of a hydronium ion(H3O+). For the general acid HA, which reacts with water according to the equation HA(aq) + H2O(l) ⇄ A-(aq) + H3O+(aq), the acid ionization constant is,

K_{a}=\frac{[H_{3}O^{+}][A^{-}]}{[HA]}

acid precipitation Precipitation that is more acidic than "normal" due to the presence of acid forming gases in the atmosphere. Acid precipitation can lead to lower pH values of water bodies and increased leaching of metals from soil.
acid-base reactions

In the Bronsted-Lowry model of acids and bases, chemical reactions which transfer protons (H+ ions). The proton donor is the acid and the proton acceptor is the base.

acidic solution

A solution in which the concentration of hydronium ions (H3O+) is greater than the concentration of hydroxide ions (OH-). Acidic solutions have a pH less than 7 and a pOH greater than 7.

albedo The fraction of solar radiation reflected by the surface of an object, typically expressed as a percentage. Surfaces covered by snow have a high albedo, the albedo of soils ranges from high to low, while vegetation and oceans have a low albedo. The albedo of the Earth varies due to changes in cloud cover, snow, ice, leaf area and land use.
alternative energy source

Refers to a means of producing energy which does not require the combustion of fossil fuels. Examples include wind, solar, nuclear and hydroelectric.

amount of substance

The quantity of a substance, measured in mass, volume, or moles. Chemists use moles of a substance as it reflects the actual number of particles (atoms, molecules, or ions) involved.

amphoteric A substance that can act both as an acid and as a base, depending on the surrounding environment.
anaerobic Occurring in the absence of oxygen.
anthropogenic

Resulting from or produced by human beings.

aquated

Dissolved in water, with individual solute molecules surrounded by water molecules to minimize electrostatic potential energy.

aragonite A polymorph of calcium carbonate, which some marine animals use to form their external shells.
atmosphere

The gaseous envelope surrounding the Earth containing nitrogen gas (78%), oxygen gas (21%) and a number of other trace gases.

atmospheric lifetime A measure of the length of time that a gas molecule spends in the atmosphere. This amount of time depends on the amount of gas in the atmosphere, as well as it's rate of release to, or loss from, the atmosphere. Atmospheric lifetimes range from hours to weeks for active and reactive pollutant's (e.g., ozone and sulfate aerosols) to more than a century for relatively inert gases (e.g., chlorofluorocarbons, carbon dioxide). In reference to greenhouse gases, atmospheric lifetime can refer to the approximate amount of time it would take for the anthropogenic portion of a greenhouse gas concentration to return to its natural level by either being converted to another chemical compound or being taken out of the atmosphere by other processes.
atomic number The number of protons contained within the nucleus of an atom for a given element. The atomic number determines the identity of the element. Given the symbol Z.
atomic weight Also called atomic mass, it is the average relative atomic mass of the atoms of an element in a sample, weighted by the relative abundances of each isotope of the element.
base Any substance that acts as a proton acceptor, in the Bronsted-Lowry model of acids and bases.
base ionization constant The equilibrium constant for the reaction of a base with water, given the symbol Kb. For the general base B, which undergoes the reaction B(aq) + H2O(l) ⇄ BH+(aq) + OH-(aq), the base ionization constant is

K_{b}=\frac{[BH^{+}][OH^{-}]}{[B]}

It can be shown that the value of Kb can be derived from the Ka of its conjugate acid from Kb= Kw/Ka.
basic solution A solution in which the concentration of hydronium ions (H3O+) is less than the concentration of hydroxide ions (OH-). Basic solutions have a pH greater than 7 and a pOH less than 7.
bomb calorimetry The technique by which the energy change of a reaction is measured at constant volume. Bomb calorimeters are typically used to measure the energy changes of combustion reactions by monitoring changes in temperature.
Bronsted-Lowry model A model of acids and bases that is centered on the transfer of protons (H+ ions). According to this model, in an acid-base reaction, a proton is transferred from an acid to a base.
Brownian motion The irregular motion of very small particles suspended in a solution. First described by Robert Brown in 1827 and mathematically described by Albert Einstein in 1905, Brownian motion provides evidence for the existence of tiny, unseen particles that possess kinetic energy.
buffer A solution containing relatively large amounts of a weak acid and its conjugate base which functions to minimize the large pH changes that would otherwise occur when a strong acid or base is added to the solution.
bulk properties of gases Macroscopic properties of gases which are independent of the type of gas, including pressure, volume, temperature, and amount of substance.
calorimeter

The device used in calorimetry to monitor temperature changes during a chemical reaction. Examples include thermally insulated containers or bomb calorimeters.

calorimetry The technique used to measure the energy change of a chemical reaction or physical process. A calorimetry experiment can be performed at constant pressure or constant volume.
carbon neutral Refers to a process that produces no net carbon emissions.
carbon sink A natural or manmade system that removes and stores carbon (carbon dioxide) from the atmosphere.
catalyst A chemical species that increases the rate at which a reaction occurs. Catalysts are regenerated after participating in a reaction.
cation

A positively charged ion. Cations have more protons than electrons.

cellular respiration

A metabolic process that oxidizes organic molecules to produce energy. The basic chemical reaction is:

C_6H_{12}O_6+6\hspace{0.5mm}O_2 \rightarrow 6\hspace{0.5mm}CO_{2}+6\hspace{0.5mm}H_{2}O+energy

collisional de-excitation The transfer of energy from one molecule to another through a collision.
conjugate acid-base pair A corresponding acid and base, which differ only by the exchange of a single proton (H+ ion). For example, CH3COOH and CH3COO- are a conjugate acid-base pair.
connectivity The pattern in which the atoms in a molecule are bonded together.
deep time The long term time frame, covering thousands to billions of years, in which scientists believe the Earth has existed. Knowledge regarding conditions over deep time is provided by sources such as ice cores and sedimentary records.
diatomic molecule A molecule made up of two atoms.
diprotic acid An acid that can donate two protons (H+ ion).
dissolution A process in which one substance (the solute) dissolves into another substance (the solvent), forming a solution in which solutes are surrounded on the molecular level by solvent molecules.
dynamic equilibrium A condition in which forward and reverse reactions are taking place at the rate, such that there is no net change in the amounts of reactants or products.
energy efficiency

The ratio of useful energy output compared to useful energy input. The efficiency of a process depends on the energy flow from a system that can be used to perform work as compared to the energy lost from the system as heat.

electrical energy

Energy in the form of the flow of electrons.

electrolyte

A compound that is able to conduct electricity when in solution due to the presence of ions.

electromagnetic radiation

Electromagnetic energy in the form of oscillating electric and magnetic fields. In a vacuum, electromagnetic radiation travels at the speed of light. This radiation encompasses the entire frequency range from gamma rays to radio waves, including visible light.

electromagnetic spectrum

A continuum of electromagnetic radiation ranging from low energy (long wavelength) radio waves to high energy (short wavelength) X-rays and gamma rays.

electronegativity The relative ability of an atom in a molecule to attract its bonding electrons.
electrons Negatively charged subatomic particles surrounding the nucleus of an atom. Electrons have a much smaller mass than protons and neutrons but form the majority of the physical space taken up by the atom. Changes in the arrangement and sharing of the outermost valence electrons of atoms form the basis of chemical bonding and reactions.
endothermic

Refers to a process in which energy is absorbed as heat. The reaction is accompanied by a positive enthalpy change.

energy The ability to do work.
energy balance (radiative)

The difference between the Earth's total incoming and total outgoing energy. If this balance is positive, warming occurs; if it is negative, cooling occurs. Averaged over the globe and over long time periods, this balance must be zero to maintain a stable climate. Zero balance implies that, globally, the amount of incoming radiant energy from the Sun must equal the sum of outgoing reflected radiant energy and outgoing thermal energy emitted as IR radiation from the Earth into space. Energy balance is often used interchangeably with radiation balance.

energy density The energy generated from a fuel or energy source per unit amount of the energy source.
enthalpy A property whose change is equal to the amount of heat transferred for constant pressure processes.
enthalpy change The amount of heat transferred in a constant pressure process, when no work has been performed other than the work of expanding the system.
enthalpy change of reaction The difference between the total enthalpy of the products and the total enthalpy of the reactants in a chemical reaction. The enthalpy change of reaction is equal to the energy transferred as heat during reactions performed at constant pressure. The enthalpy change of reaction is symbolized as ΔrH.
enthalpy diagram

A diagram that denotes the relative enthalpies of the reactants and products in a chemical reaction. The diagram indicates if the enthalpy change was positive or negative and if the reaction was endothermic or exothermic.

equilibrium A state of no net change, due to the equal action of opposing forces. In the case of chemical equilibrium, this refers to a state where the forward and reverse reactions are occurring at the same rate, so there is no net change in concentration of any species.
equilibrium constant The value of the reaction quotient (Q) when a reaction is at equilibrium. Given the symbol K.
evaporation

The process by which a substance transfers from the liquid phase to vapor phase.

exothermic Refers to a process in which energy is released as heat. The reaction is accompanied by a negative enthalpy change.
fossil fuels

Fuels which come from fossil carbon deposits such as coal, gas and oil.

free radical Any atom, ion or molecule that has one or more unpaired electrons.
frequency

The number of events that occur in a unit of time. If the number occurring is measured in one second, it is reported in units of Hertz (s-1).

gas chromatography An analytical technique that separates a gas mixture into its individual compounds. The compounds are separated based on their relative abilities to be moved into a passing gas stream from a solid or liquid phase.
gigatonne One gigatonne is equal to 1015 grams or one petagram, which is also equivalent to one billion, 109, tonnes
global water cycle The water cycle involves the exchange of water between the atmosphere, the cryosphere (frozen water: glaciers, ice, snow) and the hydrosphere (liquid water: lakes, rivers, oceans). Exchange processes include evaporation, precipitation, freezing, melting and runoff, among others.
greenhouse gas Gases in the atmosphere, both natural and anthropogenic, that are capable of absorbing and re-emitting infrared radiation. Water vapour, carbon dioxide, nitrous oxide, methane, ozone and CFCs are important greenhouse gases in Earth's atmosphere.
half-life (radioactive) The amount of time it takes for half of a sample of a radioactive isotope to undergo a nuclear decay event.
heat A net energy transfer from an object with a higher temperature to an object with a lower temperature. This usually results in a decrease in the average kinetic energy (temperature) of the warmer object's particles and an increase in the average kinetic energy (temperature) of the cooler object's particles. Heat is not the energy itself, but rather energy in transfer.
heating curve

A graph depicting the temperature change of a system with respect to the heat absorbed.

Hess's Law

If a reaction can be written as the sum of two or more steps, the enthalpy change of the reaction is equal to the sum of the enthalpy changes of the individual steps.

homonuclear diatomic molecules A molecule which is made up of two atoms of the same element, such as N2 or O2.
hydrogen bonds

Strong intermolecular forces that occur in substances which contain strongly polar covalent bonds involving hydrogen and an electronegative atom (oxygen, nitrogen or fluorine). In hydrogen bonding, partially positive hydrogen atom bonded to an electronegative atom is attracted to other partially negative electronegative atoms. Hydrogen bonding is an extreme form of dipole-dipole forces.

ideal gas

A molecular level model developed by chemists to explain the behaviour of gases. The molecules of an 'ideal' gas are assumed to exert no intermolecular forces on each other and to occupy no volume.

Industrial Revolution

A period of rapid industrial growth with far-reaching social and economic consequences, beginning in Britain during the second half of the eighteenth century and quickly spreading to continental Europe and the United States. The industrial revolution marks the beginning of a substantial increase in the use of fossil fuels and the emission of carbon dioxide. The terms pre-industrial and industrial refer to the period before and after 1750, respectively.

infrared (IR) radiation

The region of the electromagnetic spectrum adjacent to the red end of the visible spectrum and characterized by wavelengths longer than red light. It can be sensed by its warming affect when absorbed by an object.

infrared (IR) spectroscopy A technique that measures the absorption of infrared radiation of a sample as a function of the wavelength of the radiation. The absorption patterns reveal details about a molecule's composition. Also used to determine if a gas is a greenhouse gas.
infrared imaging camera

A camera which detects the infrared radiation emitted by objects. Because the intensity and frequency of IR radiation emitted by an object depends on the object's temperature, the camera is able to visually represent an object's temperature.

interglacial period A time in Earth's history, often lasting thousands of years, in which average temperatures are warmer and glaciers are generally retreating and do not dominate the landscape. We are currently living in an interglacial period. The previous interglacial period occurred from approximately 129-116 kya and is referred to as the Last Interglacial.
intermolecular forces Forces that act between molecules and govern the state of a substance, such as hydrogen bonds, dipole-dipole forces and dispersion (van der Waals) forces.
internal energy The total kinetic and potential energy contained in a system. Designated by the symbol U.
intramolecular forces The forces that hold atoms together within molecules. Intramolecular forces result from covalent bonds between atoms.
ionization constant for water he equilibrium constant, Kw, for the self-ionization of water: 2 H2O(l) ⇄ H3O+(aq) + OH-(aq). The value of Kw is 1.0 × 10-14 at 25 °C.
IR window regions

The two regions in which the most atmospherically abundant greenhouse gases, carbon dioxide and water, do not absorb IR. In these regions IR is able to escape into space, unless it is absorbed by another greenhouse gas. The most important IR window region covers the portion of the IR spectrum in which the Earth emits the majority of its IR radiation.

isotopes Atoms of the same element that have different numbers of neutrons.
isotope ratio

The ratio of the number of two isotopes of an element in a given sample, denoted with the symbol R. Isotopes ratios (such as (the number of hydrogen-2 atoms)/(number of hydrogen-1 atoms) in a substances, written R(2H/1H) and sometimes abbreviated 2H/1H, and similarly 18O/16O and 13C/12C for oxygen and carbon) can provide important data regarding historical temperatures and the source of carbon in the atmosphere

isotopologues Molecules that are identical except that one or more of the atoms of an element are different isotopes. For example, a water molecule containing two hydrogen-1 (1H) atoms and an oxygen-16 (16O) atom and a water molecule containing two hydrogen-1 atoms and an oxygen-18 atom are isotopologues.
Keeling Curve The longest continual set of data measuring the concentration of carbon dioxide in our atmosphere. This data set began in 1958 at the Mauna Loa observatory in Hawaii under the supervision of Charles David Keeling. image of keeling curve
Kelvin

The scientific unit of measurement for temperature, given the symbol K, where a change of 1 °C is equivalent to 1 K. Absolute zero, the temperature at which all thermal motion ceases, is the null point for this measurement. 0 K is equal to -273.15 °C.

kinetic energy The energy of motion.
kinetic molecular theory A model that represents all matter as composed of tiny particles that are in constant motion. This theory is used to explain and predict physical properties of matter.
Law of Conservation of Energy The first law of thermodynamics, which states that energy cannot be created nor destroyed. In other words, the total energy of the universe is constant.
law of equilibrium When a given reaction at a specific temperature reaches equilibrium, the concentration of reactants and products will remain constant, and the value of the reaction quotient (Q) will equal a constant value, called the equilibrium constant, K.
Le Chatelier's principle

A principle used to predict the changes in a chemical equilibrium when conditions are changed. If a chemical system in dynamic equilibrium is disturbed by changing conditions, the equilibrium will shift to counteract that change.

litmus paper

Paper which is infused with a vegetable dye and is used to test if a solution is acidic, basic or neutral. Blue litmus paper turns red in acidic solutions and red litmus paper turns blue in basic solutions.

macroscopic The view of matter that can be seen with the eye. Contrast to the molecular or particle level view of matter, which is referred to as microscopic.
mass number The sum of the number of protons and neutrons in atoms of an isotope. Given the symbol A.
mass spectrometry

A technique for measuring relative molecular mass by accelerating charged particles (ions) by an electric field and then passing the ions through a magnetic field where they are separated according to their mass to charge ratio.

model (molecular) An explanation of the molecular level nature and behavior of substances.
molar enthalpy change of fusion

The enthalpy change accompanying the conversion of 1 mol of solid to a liquid. Fusion is another word for melting.

molar enthalpy change of vaporization

The enthalpy change accompanying the evaporation of 1 mol of gas. Vaporization is another word for boiling.

mole

The unit which measures amount of substance, often abbreviated to mol. In the case of elements composed of atoms one mole is defined as the amount of atoms in exactly 12 grams of the carbon-12 isotopes.

molecular level

The portrayal of the structure, properties and behavior of tiny, unseen particles that constitute matter. Also called the particle level.

molecule A particle consisting of atoms which are covalently bonded together.
mole fraction The amount (in mol) of a particular chemical species in a mixture, divided by the sum of all the chemical species present. The mole fraction has no units. Also referred to as amount fraction
monoprotic acid An acid which can only donate a single proton (H+ ion).
Montreal Protocol

The Montreal Protocol is short for the Montreal Protocol on Substances That Deplete the Ozone Layer. It is an international treaty designed to protect the ozone layer by gradually phasing out the substances that are responsible for ozone depletion in the stratosphere. Originally signed in 1987, it has undergone several revisions since that time and is currently ratified by the majority of the nations on the planet (196 total).

net reaction The change in concentrations of reactants and products in a reaction as a result of unequal rates of the forward and reverse reactions.
neutral solution A solution in which the concentration of hydronium ions (H3O+) is equal to the concentration of hydroxide ions (OH-), resulting in a pH of 7.
neutrons Neutrally charged subatomic particles contained within the nucleus of an atom. Neutrons have about the same mass as protons and a much greater mass than electrons.
nitrogen cycle The series of processes by which nitrogen is interconverted between different chemical forms in the soil, atmosphere and living organisms.
nucleus

The dense centre of an atom, consisting of protons and neutrons. The nucleus accounts for nearly all of the mass of an atom but only a small fraction of its volume. Changes in the nucleus of an atom form the basis of nuclear chemistry and nuclear power.

partial negative charge

An area in a molecule with a higher electron density. Electrons spend more time in this area, typically around highly electronegative atoms. As a whole, the molecule is still neutral and has equal numbers of protons and electrons (so the molecule is not an ion), but certain regions of the molecule are slightly more negative or more positive.

pH

The concentration of hydronium ions in aqueous solution, expressed as a logarithmic value: pH = -log[H3O+].

pH indicator

A pH indicator is a chemical compound that changes color depending on the acidity or basicity of the solution it is added to so that the pH of the solution can be determined visually.

pH scale

A logarithmic scale used to express the wide range of concentration of hydronium ions in aqueous solutions, using the formula, pH = -log[H3O+]. The pH scale generally ranges from (1 M H3O+) to 14 (1 M OH-)

phase change Changes in the physical state of a substance between, for example, solid, liquid or gas. Phase changes do not involve any chemical reactions.
photon An individual bundle or "particle" of electromagnetic energy.
photosynthesis

The process by which plants use energy from sunlight to convert carbon dioxide (CO2) and water (H2O) to carbohydrates (e.g., C6H12O6), releasing oxygen (O2) in the process.

pOH scale A logarithmic scale used to express the concentration of hydroxide ions in aqueous solutions, using the formula, pOH = -log[OH-].
polymorph

Various solid forms of a compound with the same chemical composition. For example, two polymorphs of calcium carbonate (CaCO3) are aragonite and calcite.

polyprotic acid An acid which can donate more than one proton (H+ ion).
positive feedback loop

A process in system dynamics in which a system reacts to amplify the effects of a force that is acting upon it. An example of a positive feedback loop in the climate system is the effect of warmer temperatures on Earth's albedo. As the Earth warms, increasing temperatures may cause snow and ice cover to melt, revealing the darker land surface underneath. The darker surface absorbs more solar energy, causing further temperature increase, thus melting even more snow and ice cover.

potential energy

Energy due to the position of an object.

ppm Parts-per-million. One part out of a million parts. Often used as a unit of concentration in the measure of atmospheric trace gases.
precipitation reaction A reaction between dissolved ions to form a solid substance that is called the precipitate.
pressure The force exerted over a unit area. In kinetic molecular theory, pressure is related to the number of collisions between gas particles and the walls of the container combined with the force of these collisions.
protons Positively charged subatomic particles contained within the nucleus of an atom. Protons have about the same mass as neutrons and a much greater mass than electrons.
proxy A proxy is a record that is interpreted, using scientific principles, to represent a historical variable that cannot be directly measured. Examples of temperature proxies on Earth include tree ring records, characteristics of corals and various data derived from ice and sediment cores.
radiant energy Energy possessed by electromagnetic radiation, such as sunlight and IR radiation.
radiation balance The difference between total incoming and total outgoing radiant energy. If this balance is positive, warming occurs; if it is negative, cooling occurs. Averaged over the globe and over long time periods, this balance must be zero to maintain a stable climate. Zero balance implies that, globally, the amount of incoming solar radiation must equal the sum of outgoing reflected solar radiation and outgoing thermal infrared radiation emitted by the climate system. A perturbation of this global radiation balance is called radiative forcing.
radiative forcing A change to the balance between radiation entering and leaving the climate system. Primarily caused by substances in the atmosphere.
radioactive decay A spontaneous nuclear transformation from one element or isotope to another that occurs for some isotopes of some elements. During this process particles and/or electromagnetic radiation are emitted.
radioisotope An isotope for which radioactive decay has been experimentally detected. Radioisotopes undergo changes to their nuclei, forming new nuclei with new isotopic identities.
reaction quotient A function, given the symbol Q, defined to express the ratio between the concentrations of reactants and products during a reaction. For the general chemical equation aA + bB  ⇄ cC + dD the reaction quotient is,

At equilibrium, the value of the reaction quotient is constant for a specific temperature and is called the equilibrium constant, K.
relative atomic mass

The mass of an atom of a certain isotope relative to the mass of carbon-12, which is defined as exactly 12.

rotational Refers to the motion of an object that is spinning (rotating).
ruminant animals A group of mammals, including the cow, sheep, buffalo and goat, which possess four stomachs and regurgitate undigested food from their first stomach. This process is known as chewing cud. They live in a symbiotic relationship with microorganisms in their digestive tract that enable them to digest cellulose, releasing methane in the process.
saturated solution

A solution in which no more solute can dissolve. The solid, liquid or gaseous solute is in dynamic chemical equilibrium with the dissolved species.

saturation horizon

The depth at which the ocean transitions from supersaturation in the upper ocean to unsaturation in the deep ocean.

self-ionization A reaction in which two identical molecules react to produce ions. In the self-ionization of water, a proton is transferred between two water molecules to produce a hydronium ion (H3O+) and a hydroxide ion (OH-).
solubility The concentration of a dissolved substance (the solute) in a saturated solution, at a specific temperature.
solubility product

The equilibrium constant of a dissolution reaction, given the symbol Ksp. When the reaction quotient, Q, reaches the solubility product, Ksp, the solution is saturated.

soluble The extent to which a compound will dissolve in solution.
solution

A homogenous molecular level mixture consisting of a substance in which some other substance is dissolved. The dominant substance is called the solvent and the dissolved substance is called the solute. The solvent molecules surround solute molecules, which are then said to be solvated, or dissolved. In aqueous solutions, the solvent is water.

solution calorimetry The technique by which the enthalpy change of a reaction is determined. The reaction is performed in solution, at constant pressure, and the temperature change of the water is used to calculate the enthalpy change of the reaction.
speciation The speciation of an element is the distribution of an element among defined chemical species in a system.
speciation plot (pH) A graph displaying the changes in relative concentrations of an acid and its conjugate base, expressed as a percentage (or fractional abundance) of the total, as pH changes.
species In chemistry, any group of particles that behave identically. For example, a species of carbon is hydrogen carbonate (HCO3-).
specific heat capacity The amount of heat required to raise the temperature of 1 g of a substance by 1 K (in J K-1 g -1). Substances with high specific heat capacities must absorb a large amount of heat before their temperature increases significantly; substances with low specific heat capacities will experience a substantial temperature increase when absorbing only a small amount of heat.
stable isotope An isotope for which no radioactive decay has been experimentally detected. Stable isotopes do not undergo nuclear changes.
standard atomic weights The values of relative atomic masses recommended by the IUPAC Commission on Atomic Weights and Isotopic Abundances and which apply to elements in any normal sample.
standard molar enthalpy changes of formation The enthalpy change that occurs when 1 mole of a substance is formed from its elements under standard conditions.
stratosphere The second layer of the atmosphere above the surface of the Earth. Most of the photochemical reactions involving ozone occur here.

layers of the atmosphere

strong acid An acid that is a strong electrolyte and ionizes completely in aqueous solution.
strong base

A base that is a strong electrolyte and ionizes completely in aqueous solution.

supersaturated

A solution in which the concentration of dissolved species is greater than the concentration in a saturated solution and precipitation of the ions into a solid and/or phase separation should occur. The reaction quotient is greater than the solubility product.

surroundings Everything external to the object of focus.
system The object of focus.
temperature A measure of the average kinetic energy of the particles in a system. If, on average, the particles are moving faster, the temperature is higher.
temperature profile (atmospheric) How temperature in the atmosphere changes, as altitude increases.
thermal energy

The total kinetic energy of the atoms, ions or molecules in a system.

thermal expansion The tendency of matter to change in volume in response to a change in temperature. When a substance is heated, the particles begin moving more rapidly and become more separated from each other, leading to expansion.
thermochemistry The study of energy transfers in chemical reactions.
trace gases Gases which are found in Earth's atmosphere at very low concentrations. Essentially any atmospheric gas, other than N2 and O2.
translational Refers to motion from one position to another through space.
troposphere The first layer of the atmosphere above the surface of the Earth. 85% of the mass of the entire atmosphere is found here.

layers of the atmosphere

ultraviolet (UV) radiation

The region of the electromagnetic spectrum adjacent to the violet end of the visible spectrum and characterized by wavelengths shorter than violet light. UV radiation has been linked to skin cancer and chronic exposure to certain frequencies of UV radiation can damage DNA. In the stratosphere, ozone prevents much of the incoming UV radiation from reaching the Earth.

vibration

In a molecule, the repetitive stretching, bending or twisting of bonds between adjacent atoms.

vibrational Refers to the relative motion of atoms within a molecule due to the stretching, bending, or twisting of bonds.
volume The space occupied by something.
wavelength

One wavelength is the distance between two identical points on adjacent oscillations along a wave

wavenumbers A measure of the number of waves in unit of distance. Wavenumber is inversely proportional to wavelength, as shorter wavelengths will have more waves per unit of distance.
weak acid

An acid that is a weak electrolyte and does not ionize completely in aqueous solution. The strengths of weak acids are expressed as Ka and pKa values.

weak base A base that is a weak electrolyte and does not ionize completely in aqueous solution. The strengths of weak bases are expressed as Kb and pKb values.
work

Force applied over a distance (work=force × distance). Energy can be supplied to a system as work, which increases the internal energy of the system.

work of expansion

Work that is performed as a system expands by pushing against the surrounding air molecules.