Exam 2 CHEM-UA-125

oxidation-reduction reaction (redox reaction)

process in which there is a net movement of electrons from one reactant (reducing agent) to another (oxidizing agent).

oxidation

The loss of electrons by a species, accompanied by an increase in oxidation number.

reduction

The gain of electrons by a species, accompanied by a decrease in oxidation number.

oxidizing agent

The substance that accepts electrons in a reaction and undergoes a decrease in oxidation number.

reducing agent

The substance that donates electrons in a redox reaction and undergoes an increase in oxidation number.

oxidation number (oxidation state)

A number equal to the magnitude of the charge an atom would have if its shared electrons were transferred to the atom that attracts them more strongly.

dynamic equilibrium

The condition at which the forward and reverse reactions are taking place at the same rate, so there is no net change in the amounts of reactants or products.

double replacement (metathesis reaction)

A reaction in which atoms or ions of two compounds exchange bonding partners. Precipitation and acid-base reactions are examples.

pressure (P)

The force exerted per unit of surface area.

barometer

A device used to measure atmospheric pressure. Most commonly, a tube open at one end, which is filled with mercury and inverted into a dish of mercury.

manometer

A device used to measure the pressure of a gas in a laboratory experiment.

Pascal (Pa)

The SI unit of pressure; 1 Pa = 1 N/m2.

standard atmosphere (atm)

The average atmospheric pressure measured at sea level and 0°C, defined as 1.01325 × 105 Pa.

millimeter of mercury (mmHg)

A unit of pressure based on the difference in the heights of mercury in a barometer or manometer. Renamed thetorrin honor of Torricelli.

ideal gas

A hypothetical gas that exhibits linear relationships among volume, pressure, temperature, and amount (mol) at all conditions; approximated by simple gases at ordinary conditions.

boyles law

The gas law stating that, at constant temperature and amount of gas, the volume occupied by a gas is inversely proportional to the applied (external) pressure:V∝ 1/P.

charles's law

The gas law stating that, at constant pressure, the volume occupied by a fixed amount of gas is directly proportional to its absolute temperature:V∝T.

absolute zero

Theoretically the lowest attainable temperature (0 K or −273.15°C ).

Avogadro's Law

The gas law stating that, at fixed temperature and pressure, equal volumes of any ideal gas contain equal numbers of particles, and, therefore, the volume of a gas is directly proportional to its amount (mol):V∝n.

standard temperature and pressure (STP)

The reference conditions for a gas: 0°C (273.15 K) and 1 atm (760 torr).

standard molar volume

The volume of 1 mol of an ideal gas at standard temperature and pressure: 22.4141 L.

Ideal Gas Law

(alsoideal gas equation) An equation that expresses the relationships among volume, pressure, temperature, and amount (mol) of an ideal gas:PV=nRT.

Universal Gas Constant (R)

A proportionality constant that relates the energy, amount of substance, and temperature of a system;R= 0.0820578 atm·L/mol·K = 8.31447 J/mol·K.

Partial Pressure

The portion of the total pressure contributed by a gas in a mixture of gases.

Dalton's Law of Partial Pressures

A gas law stating that, in a mixture of unreacting gases, the total pressure is the sum of the partial pressures of the individual gases:Ptotal =P1 +P2 +P3 + ⋅⋅⋅.

Mole Fraction (X)

A concentration term expressed as the ratio of number of moles of solute to the total number of moles (solute plus solvent).

Kinetic Molecular Theory

The model that explains macroscopic gas behavior in terms of particles in random motion whose volumes and interactions are negligible.

rms (root-mean-square) speed (urms)

The speed of a molecule having the average kinetic energy; very close to the most probable speed.

effusion

The process by which a gas escapes from its container through a tiny hole into an evacuated space.

Graham's law of effusion

A gas law stating that the rate of effusion of a gas is inversely proportional to the square root of its density (or molar mass):

Diffusion

The movement of one fluid through another.

mean free path

The average distance a particle travels between collisions at a given temperature and pressure.

Collision Frequency

The average number of collisions per second that a particle undergoes.

van der Waals equation

An equation that accounts for the behavior of real gases.

van der Waals constants

Experimentally determined positive numbers used in the van der Waals equation to account for the interparticle attractions and particle volume of real gases.

system

The defined part of the universe under study.

surroundings

All parts of the universe other than the system being considered.

internal energy

The sum of the kinetic and potential energies of all the particles in a system.

heat

(also thermal energy) The energy transferred between objects because of a difference in their temperatures only.

Exothermic Process

A process that occurs with a release of heat to the surroundings and therefore a decrease in the enthalpy of the system (ΔH< 0).

Endothermic Process

A process that occurs with an absorption of heat from the surroundings and therefore an increase in the enthalpy of the system (ΔH> 0).

work

The energy transferred when an object is moved by a force.