Standard Atmospheric Pressure -
Corresponds to the typical pressure at sea level.
pressure is equal to 1.01325 x 10
Pa, 760 mm Hg, 760 torr, 1 atm, and 101.325 kPa
10.3 The Gas Laws
The four variables needed to define the physical state of a gas are temperature, T, pressure, P,
volume, V, and the amount of gas, which is usually expressed in moles, n.
Boyle's Law -
The volume of a fixed quantity of gas maintained at constant temperature is
inversely proportional the pressure. V = constant x 1/P; PV = constant.
Charles' Law -
The volume of a fixed amount of ga maintained at constant pressure is directly
proportional to its absolute temperature (on the Kelvin scale).
V = constant x T; V/T = constant
Avogadro's Hypothesis -
Equal volumes of gases at the same temperature and pressure
contain equal number of molecules.
was established, which said
volume of a gas maintained at constant temperature and pressure is directly proportional to the
number of moles of the gas.
law of combining volumes
, provided the basis for both
of these, which said that at a given temperature and pressure the volumes of gases that react
with on another are in the ratios of small whole numbers.
10.4 The Ideal-Gas Equation
The Ideal-Gas Equation -
PV = nRT; Made by combining the three gas laws, An
hypothetical gas whose pressure, volume, and temperature behavior is completely described by
the ideal-gas equation.
is called the
, whose value depends on the
units of P,V, n, and T.
Temperature is expressed in Kelvins, Pressure in atm's, Volume in liters,
and the quantity of gas,
, in moles.
Standard Temperature and Pressure (STP) -
0 degrees Celsius and 1 atm.
10.5 Further Applications of the Ideal-Gas Equation
The ideal gas law can also be used to determine the density of a gas, by multiplying both
sides of the equation (n/V) = (P/RT) by M, the molar mass, which is the number of grams in one
mole of a substance. The resulting equation (nM/V) is equivalent to m/V (mass divided by
volume), which is the same thing as density.
Thus, the density of gas is given by the equation
10.6 Gas Mixtures and Partial Pressures
Dalton's Law of Partial Pressures -
The total pressure of a mixture of gases equals the sum of
the pressures that each would exert if it were present alone.
The pressure exerted by a particular
component of a mixture of gass is called the
The law has the equation P
(RT/V), where P
is the total pressure exerted by the gas(es), and n
is the total number of moles
in the gas(es)
Partial Pressures and Mole Fractions -
Because each gas in a mixture behaves independently,
we can relate the amount of a given gas in a mixture to its partial pressure.
For a mixture, n
called the mole fraction of gas 1, which is denoted as X
X, expresses the
ratio of the number of moles of one component to the total number of moles in the mixture.