Chapter 6: the gaseous state Flashcards
gases have similar .., which allows us to develop models to predict their …
physical behaviors; properties
a gas is a fluid with no definite … or fixed …
shape; volume
a gas fills the
total volume of its container
because a gas is mostly empty space, a gas is
compressible
the volume of a gas … when an external force is applied
decreases
a liquid is a fluid with a
fixed volume but no definite shape
a liquid takes the …., but it does not…
shape of its container; expand to fill the container
a solid has both fixed … and …
shape; volume
liquids and solids are …
condensed phases
condensed phases: phases that are resistant to … because the spaces between the particles are … and cannot ….
volume changes; small; readily change
because the individual particles in both the liquid and solid phases are …., but in the gas phase are …, the density of the gas phase is much … than the density of either of the condensed phases
closely packed; separated; lower
density is generally expressed in .. for a gas, but the densities of liquids and solids are expressed in …
grams per liter; grams per milliliter
when a gas under atmospheric conditions condenses to a solid or a liquid, the density increases by a fact of about
1000
liquids and solids are resistant to volume changes because the spaces between the particles are
small and cannot readily change
pressure is defined as the
force exerted on a surface divided by the area of the surface
the atmosphere exerts a pressure because of the
weight of the gas molecules in the air
a barometer measures the
pressure of the amosphere
gravitational attraction pulls down the column of mercury, leaving a … above it in the tube. the column stops falling when the pressure caused by the weight of the mercury is
vacuum; equal to the pressure exerted by the atmosphere
mercury level in barometer rises→
high pressure
mercury level in barometer lowers→
low pressure
mercury is used in barometers because it is a liquid with a
high density
a manometer measures pressure
differences
(manometer) the atmosphere exerts a … on the mercury surface at the open end of the tube, and the gas within the container exerts pressure on the …
pressure; other surface of the mercury
(manometer) the difference between the heights of the 2 mercury surfaces corresponds to the difference between the
gas pressure in the container and the atmospheric pressure
for a closed-end manometer the pressure of the gas is … to the difference between the heights of the …
equal; two mercury surfaces
si unit for pressure
pascal
1 pa = 1 N/ m^2 =
1 kg/ m * s^2
1 bar =
10^5 Pa
1 atm= … mm Hg
760
1 torr = … Pa
133.3
1 atm= … torr
760
1 atm= … psi
14.7
psi is
pounds per square inch
1 atm= … kPa
101.325
1 atm= … bar
1.01325
1 atm= …. in Hg
29.92
the physical properties of all gases behave in the …, regardless of the …
same general manner; identity of the gas
4 independent properties that define the physical state of a gas:
pressure; volume; temperature; number of moles
gas laws express the relationships between the
4 independent properties of gases
volume of a gas increases as pressure
decreases
boyle’s law states that at constant …, the … of a sample of gas is … proportional to the …
temperature; volume; inversely; pressure
V=
constant X 1/P
PV=
constant
P1V1=
P2V2
doubling the temperature causes the volume of the gas to
double
charles’s law states that at constant …, the … of a fixed amount of gas is … to the absolute …
pressure; volume; directly proportional; temperature
V = (charles’s law)
constant * T
at absolute zero the volume of the gas must be
zero
at absolute zero the volume of gas is zero because all gases …. before they reach this temperature
condense to liquid/solid phase
absolute zero: … degrees C; … K
-273.15; 0
V/T =
constant
V1/T1=
V2/T2
avogadro proposed that at thes ame temperature and pressure, equal volumes of gases contain the
same number of particles
avogadro;s law states that at constant pressure and temperature, the volume of a gas sample is …
proportional to the number of moles of gas present
(avogadro’s law) V=
constant * n
V1/n1 =
V2/n2
combined gas law:
P1V1/n1 = P2V2/n2
temps must be expressed in
kelvins
R with units Latm/ molK
0.08206
R with units kgm^2/s^2mol*K
8.314
R with units J/mol*K
8.314
R with units cal/mol*K
1.987
SCUBA:
self-contained underwater breathing apparatus
high pressures caused by water at depths greater than … starts to force more nitrogen gas to …. leading to a state of motor function loss, decision making inability, and impairment in judgment known as …
50 m; dissolve into the bloodstream and other tissues; nitrogen narcosis
the bends: a diver ascends toward the surface too quickly and nitrogen …. which then collect in the … causing extreme pain and the body …
bubbles come out of the body tissues; joints; curls up
reaction in air bags
decomposition of sodium azide
divers use an air mix that contains a lot of … gas, because helium doesn’t …
helium; dissolve in body tissues to a large extent
divers can also use air mixes that contain …, but this can cause …, which thus results in uncontrollable …
heliox; high-pressure nervous syndrome; shaking
trimix: mixture of … o2, … n2, and … He
10%; 20%; 70%
ideal gas law:
PV=nRT
R is the
ideal gas constant
the value of the constant R is determined
experimentally
measurements show that the volume of 1 mol of an ideal gas at standard temperature and pressure is
22.41 L
standard temperature and pressure:
1 atm; 0 degrees C/273K
the ideal gas law expresses the interrelationships of
volume, pressure, amount, and temperature
we use the term ideal because under certain conditions the behavior of gases
deviates from that predicted by the ideal gas law
the idea gas law is used to determine the value of any of the four properties–…., given values of the other three
pressure, volume, amount, and temperature of a gas
before the development of mass spectrometry, the molar masses of many substances were determined by using the
ideal gas law
the … of any given gas under a fixed set of conditions is also calculated from the ideal gas law
density
at constant pressure and temperature, the density of a gas is directly related to its
molar mass
just as in solution, reacting species in the gas phase can readily …, a necessary requireent for reactions to occur
collide
use the ideal gas law to convert the moles of a gas sample to its
equivalent volume
in chemical reactions at constant temp and pressure, the volumes of gases combine in the
same proportions as the coefficients of the equation
we can directly calculate the volume of a gas produced b a reaction of gases in a chemical reaction, as long as the
pressure and temperaure of the gases are the same
we do not need a pue sample of gas to use the
ideal gas law
many of the early experiments that led to the formulation of the gas laws were performed with samples of
air rather than pure substances
In 1801, English scientist John dalton realized that each gas in a mixture of gases exerts a pressure, called a …, which is the same as if the gas…
Partial pressure; occupied the container by itself
Dalton’s law of partial pressure:
Pt = Pa + Pb
A mixture of gases is a
Solution
A convenient concentration unit to describe this gaseous mixture is the
Mole fraction
Mole fraction: the number of moles of one component of a mixture divided by
The total number of moles of all substances present in the mixture
χa =
Moles of component A/ total moles of all substances
χa=
nA/ ntotal
χa+χb+χc+….+χn=
1
Pa =
χa x Pt
chemists measure the volume of a gas generated in a reaction by
determining the volume of water displaced
the gas sample collected by displacement of water is not pure, because some
water molecules are also present in the gas phase
the partial pressure of water present in the gas phase depends on the
temperature of the water
to determine the partial pressure of the gas collected, you must subtract the partial pressure of the water vapor from the
total pressure
scientists made measurements of volumes and temperatures of gases to show that the volume of a gas at constant pressure is
proportional to its temperature in kelvins
chemists sought to understand why a single law can describe the physical behavior of
all gases, regardless of the nature/size of the gas particles
kinetic molecular theory describes the
behavior of gas particles at the molecular level
(4 postulates of kinetic theory) a gas consists of … that are in … and …. no …. exist between any two gas particles
small particles; constant; random motion; forces of attraction or repulsion
(4 postulates of kinetic theory) gas particles are very … compared with the ….
small; average distance that separates them
(4 postulates of kinetic theory) collisions of gas particles with … and with the …. are …
each other; walls of the container; elastic
(4 postulates of kinetic theory) elastic: no loss in … when …
total kinetic energy; particles collide
(4 postulates of kinetic theory) the average kinetic energy of gas particles is proportional to the
temperature on the kelvin scale
(kinetic molecular theory) the particles occupy only a small part of the ….; most of the … is …
volume of the container; volume; empty space
(kinetic molecular theory) the gas particles are in
constant motion
(kinetic molecular theory) the … and … of the particles change when they collide, but the … does not change
direction; speed; total energy of the gas
(kinetic molecular theory) the energy of the gas changes only if the
temperature changes
(kinetic molecular theory) the kinetic molecular theory assumes that the pressure exerted by a gas comes from the
collisions of the individual gas particles with the walls of the container
(kinetic molecular theory) pressure increases if the … or …. increases, because both will increase the … on the wall
energy of the collisions; the number of wall collisions per second; force
the kinetic molecular theory is consistent with the
ideal gas law
as the size of a container decreases (at constant temperature), the number of … of the gas particles with the …. during any time interval …, because the particles have less … between collisions with the walls
collisions; walls per unit area; increases; distance to travel
at constant temperature, the average force of each collision …, but in a smaller volume, the same number of particles strike a given area of the wall …, so the pressure of gas in the container …
does not change; more often; increases as volume decreases
with an increase in temp and thus an increase in kinetic energy, each collision exerts a …, and the number of collisions per unit area per time …
greater force on the walls; increasese
if pressure is to remain constant, the size of the container must …, reducing the number of these more …
increase; energetic collisions per unit area
increasing the number of gas particles in a container increases the
number of collisions with the walls per unit area per unit time
not all gas particles move at the same
speed
the relationship of the average kinetic energy of the gas particles to the speed (u) of the particles is:
KE= 1/2mu^2
note: KE and u have lines over them, indicating that they are averages
the square root of u^2 (u with a line over it) is called the …, labeled …, and is used to indicate the …
root-mean-square (rms) speed; urms; average speed of a gas
from the mathematical treatment of the kinetic theory of gases, we can determine the
relative number of gas particles that have any particular speed
root mean square speed is not the same as the
most probable speed (maximum of graph)
plots that show speed and number of particles:
maxwell-boltzmann distribution curves
if the temperature increases, the … increases, the curve …, and both the most probable speed and urms shift to …
average speed; broadens; greater values
the average kinetic energy of the gas particles is proportional to the .., and kinetic molecular theory predicts that the rms speed is related to … and … by the equation:
temperature; temperature; molar mass;
urms=√(3RT)/M
R in the urms calculation is
8.314 J/molK
molar mass in urms is expressed n
kilograms per mole
the rms speed of a gas sample is proportional to the square root of … and inverely proportion al to the square root of …
temperature; molar mass
at constant temp, gases with greater maolar masses ave lower
rms speeds
the observation that heavier particles have lower rms speeds is expected because the molecules in a heavier sample must move more … as thea verage kinetic energies of all gases are the .. at a given temperature
slowly; same
diffusion is the
mixing of particles caused by motion
the faster the molecular motion, the faster a gas
diffuses
the rate of diffusion is always less than the …, because collisions prevent the particles from ..
rms speed of the gas; moving in a straight line
effusion is the passage of a gas through
a small hole into an evacuated space
graham’s law states that the rte of … of a gas is … to the square root of its …
effusion; inversely proportional; molar mass
the kinetic molecular theory explains graham’s law because the rms speed of the gas particles is inversely proportional to the
square root of their molar mass
rate of effusion of gas a/ rate of effusion of gas B =
√(molar mass of B/ molar mass of A)
gases with greater rates of effusion escape through the hole in
shorter lengths of time
the time it takes for a gas to effuse, t, is .. to the rate of effusion
inversely proportional
most gases obey the ideal gas law quite closely at a pressure o about … and a temperature well above the … of the substance
1 atm; boiling point
for a gas that follows the ideal gas law, the measured values of PV/nRT graph to a
straight line equalling 1
as the pressure increases to high values, … occur
deviations
deviations from the ideal gas law occur under extreme conditions because two of the assumptions of the kinetic molecular theory simply are nto correct when
gas particles are close together
these assumptions are: that gas particles are …; that no … exist between gas particles
small compared with the distances separating them; attractive forces
at high pressure, the volume occupied by the individual individual particles is no longer negligible coompared with the
volume of the gas sample
when the particle’s size is no longer negligibl, the actual volume available for the gas particles to move is
reduced
gas particles that are attracted to each other do not … as … as predicted, reducing he … below that predicted by the ideal gas law
strike the wall; hard; pressure
as the pressure increases, he particles are forced …, making this attractive interaction more important because because more gas particles are …
closer together; close to the one about to hit the wall
at very high pressures, the effect of molecular volume is greater than that of
the attractive forces
a gas deviates from the ideal gas law at … and … near the … and at very high …
temperatures; pressures; condensation point; high pressures
the ideal gas law can be modified to include the effects of
attractive forces and the volume occupied by the particles
van der waals equation: nRT-
(P + an^2/V^2)(V-nb)
n: number of
moles
b: constant that depends on the
size of the gas particles
a: constant related to the strength of the
attractive forces
