University Physics Volume 2

# Key Terms

### Key Terms

$NA,NA,$ the number of molecules in one mole of a substance; $NA=6.02×1023NA=6.02×1023$ particles/mole
Boltzmann constant
$kB,kB,$ a physical constant that relates energy to temperature and appears in the ideal gas law; $kB=1.38×10−23J/KkB=1.38×10−23J/K$
critical temperature
$TcTc$ 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 $R=NAkBR=NAkB$
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
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