Key Terms

Key Terms

Avogadro’s number

$N_{\text{A}},$ the number of molecules in one mole of a substance; $N_{\text{A}}=6.02\times {10}^{23}$ particles/mole

Boltzmann constant

$k_{\text{B}},$ a physical constant that relates energy to temperature and appears in the ideal gas law; $k_{\text{B}}=1.38\times {10}^{\mathrm{-23}}\text{J/K}$

critical temperature

$T_{\text{c}}$ at which the isotherm has a point with zero slope

Dalton’s law of partial pressures

physical law that states that the total pressure of a gas is the sum of partial pressures of the component gases

degree of freedom

independent kind of motion possessing energy, such as the kinetic energy of motion in one of the three orthogonal spatial directions

equipartition theorem

theorem that the energy of a classical thermodynamic system is shared equally among its degrees of freedom

ideal gas

gas at the limit of low density and high temperature

ideal gas law

physical law that relates the pressure and volume of a gas, far from liquefaction, to the number of gas molecules or number of moles of gas and the temperature of the gas

internal energy

sum of the mechanical energies of all of the molecules in it

kinetic theory of gases

theory that derives the macroscopic properties of gases from the motion of the molecules they consist of

Maxwell-Boltzmann distribution

function that can be integrated to give the probability of finding ideal gas molecules with speeds in the range between the limits of integration

mean free path

average distance between collisions of a particle

mean free time

average time between collisions of a particle

mole

quantity of a substance whose mass (in grams) is equal to its molecular mass

most probable speed

speed near which the speeds of most molecules are found, the peak of the speed distribution function

partial pressure

pressure a gas would create if it occupied the total volume of space available

peak speed

same as “most probable speed”

pV diagram

graph of pressure vs. volume

root-mean-square (rms) speed

square root of the average of the square (of a quantity)

supercritical

condition of a fluid being at such a high temperature and pressure that the liquid phase cannot exist

universal gas constant

R, the constant that appears in the ideal gas law expressed in terms of moles, given by $R=N_A{k}_B$

van der Waals equation of state

equation, typically approximate, which relates the pressure and volume of a gas to the number of gas molecules or number of moles of gas and the temperature of the gas

vapor pressure

partial pressure of a vapor at which it is in equilibrium with the liquid (or solid, in the case of sublimation) phase of the same substance