Ch 11 Section 3 Flashcards
joseph gay-lussac observed that 2 L of hydrogen can react with 1 L of oxygen to form 2 L of water vapor at
constant temperature and pressure
Lussac’s reaction shows a simple and definite 2:1:2 relationship between the volumes of the
reactants and the product
two volumes of hydrogen react with 1 volume of oxygen to produce 2 volumes of
water vapor
the 2:1:2 relationship for this reaction applies to any
proportions for volume
gay-lussac also noticed simple and definite proportions by
volume in other reactions of gases
Gay-Lussac’s law of combining volumes of gases states that at constant temperature and pressure, the volumes of gaseous reactnats and products can be expressed as
ratios of small whole numbers
law of combining volumes of gases as well as avogadro’s insight provided a better understanding of how gases react and
combine with each other
in 1811, avogadro found a way to explain Gay-Lussac’s simple ratios o combining volumes without violating Dalton’s idea of
indivisible atoms
avogadro rejected dalton’s idea that reactant elements are always in monatomic form when they
combine to form products
avogadro’s law states that equal volumes of gases at the same temperature and pressure contain
equal numbers of molecules
avogadro reasoned that molecules combining to form products could contain more than one
atom
at the same temperature and pressure, the volume of any given gas varies directly with the number of
molecules
avogadro’s law indicates that gas volume is directly proportional to the amount of
gas, at a given temp and pressure
V=
kn
avogadro’s reasoning applies to the combining volumes for the reaction of hydrogen and oxygen to form
water vvapor
while dalton thought the formula of water was HO, avogadro’s reasoning established that the formula must be
h2o
the coefficients in a chemical reaction involving gases indicate the relative numbers of …, the relative numbers of …, and the relative
molecules; moles; volumes
experiments eventually showed that all elements that are gases near room temp, except noble gases, normally exist as
diatomic molecules
according to avogadro’s law, one mole of any gas will occupy the same volume as one mole of any other gas at the same
temperature and pressure, despite mass differences
the volume occupied by one mole of a gas at STP is known as the
standard molar volume of a gas and is 22.4 L
knowing the volume of a gas, you can use 1 mol/ 22.4 L as a conversion factor to find the
number of moles, and mass, of a given volume of a given gas at STP
you can use the molar volume of a gas to find the volume, at STP, of a known number of
moles or a known mass of a gas
for gaseous reactants or products, coefficients in chemical equations not only indicate molar amounts and mole ratios but also reveal
volume ratios, assuming conditions remain the same
the ideal gas law is the mathematical relationship among
pressure, volume, temperature, and the number of moles of a gas
ideal gas law: PV=
nRT
ideal gas law reduces to boyles’s law, charles’s law, gay-lussac’s law, or avogadro’s law when the appropriate variables are
held constant
the number of molecules or moles present will always affect at least one of the other
three quantities
the collision rate of molecules per unit area of container wall depends on the number of
molecules present
if the number of molecules is increased for a sample at constant volume and temperature, the
collision rate increases and so does pressure
according to avogadro’s law, if pressure and temp were kept constant while number of molecules increased, the
volume would increase
an increase in volume keeps the pressure
constant at constant temperature
increasing volume keeps the collision rate per unit of wall area
constant
the constant R is known as the
ideal gas constant
the value of r depends on the units chosen for
pressure, volume, and temperature
measured values of P, V, T, and n for a gas at near-ideal conditions can be used to calculate
R
R is used in calculations when volume is in … and temp is in
liters; kelvins
ideal gas law can be applied to determine existing conditions of a gas sample when 3 of the 4 variables P,V, T, or n are
known
ideal gas law can also be used to calculate the
molar mass or density of a gas sample
for mm hg, r is
62.4
for atm, r is
.082
for J and kPa, R is
8.314
