Gases

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Gases
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States of Matter States of Matter States of Matter

A Solid - occupies a definite volume and has a definite shape.. -atoms are in close contact - occupies a definite volume and has a definite shape.. -atoms are in close contact
A Liquid - has a specific volume but it assumes the shape of its container. - it has a ability to flow -the distances between atoms are greater than in a solid - has a specific volume but it assumes the shape of its container. - it has a ability to flow -the distances between atoms are greater than in a solid
a Gas - has neither a shape of its own nor fixed volume. It takes the shape and volume of its container. - Gas mixtures are always homogeneous - Gases are highly compressible. - The molecules of a gas are relatively far away each other. - Individual gas molecules have little interaction with their neighbors. - Gas molecules move freely in every dimension of space randomly - has neither a shape of its own nor fixed volume. It takes the shape and volume of its container. - Gas mixtures are always homogeneous - Gases are highly compressible. - The molecules of a gas are relatively far away each other. - Individual gas molecules have little interaction with their neighbors. - Gas molecules move freely in every dimension of space randomly
Number of gas substances are few, Number of gas substances are few, Number of gas substances are few,

vaporization is a process in which liquid molecules turn into vapor is a process in which liquid molecules turn into vapor
condensation is a process in which gas molecules return from vapor to the liquid is a process in which gas molecules return from vapor to the liquid
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Pressure is a force per unit area. For
gas, F
P -------
A Force (massacceleration) or Fma F orce
is expressed in Newtons (N) and area is expressed
in square meters (m2) The SI unit of pressure is
N/m2 is called Pascal (Pa) For
liquid
P g h d g gravitational force 9.81
m/s2 h height of a column d
density of a liquid
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Atmospheric pressure is measured by a mercury
barometer.
At sea level, The standard atmospheric pressure
is the pressure sufficient to support a column of
mercury 760mm in height.
1.0 atm 760 mmHg 760 torr 1.01325 bar
1.01325x105 Pa
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In the laboratories, the gas pressures is
measured by manometer.
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question what is the height of a column of
water that exerts the same pressure as acolumn of
mercury 76.00cm high? Density of mercury is
13.6g/ml question a) convert to 0.357 atm
to bar. b) convert 147200 Pa to torr
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Gas laws Gas laws
Amount of gas, volume of gas, temperature and pressure are the fundamentals properties to determine the physical behavior of a gas. Amount of gas, volume of gas, temperature and pressure are the fundamentals properties to determine the physical behavior of a gas. Amount of gas, volume of gas, temperature and pressure are the fundamentals properties to determine the physical behavior of a gas.

Boyles law (the pressure-volume relationship) For a fixed amount of gas at a constant temperature, the gas Volume is inversely proportional to the gas Pressure. For a fixed amount of gas at a constant temperature, the gas Volume is inversely proportional to the gas Pressure.

Charless Law The temperature - volume relationship The Volume of a fixed amount of a gas at a constant pressure is directly proportional to its absolute (Kelvin) Temperature. The Volume of a fixed amount of a gas at a constant pressure is directly proportional to its absolute (Kelvin) Temperature.

Avagadros law ( the mole-volume relationship) The volume of a gas varies directly with its molar amount at constant temperature and pressure. The volume of a gas varies directly with its molar amount at constant temperature and pressure.
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• Boyle 1662

Pinitial . Vinitial constant Pfinal . Vfinal
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Charles 1787 Gay-Lussac 1802
Vinitial Vfinal -----------
---------- Tinitial Tfinal
In 1848 William Thomson (Lord Kelvin) proposed an
absolute temperature scale known as Kelvin scale.
On this scale 0K is called absolute zero,
equals -273.15C. T (K) t ( ?C) 273.15
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the standard temperature for gases is defined as
0 ?C273.15K and the standard pressure is defined
as 1atm760mmHg. These Standard conditions are
usually abbreviated as STP.
P 1 atm 760 mm Hg T 0C 273.15 K
At 1.0 atmosphere pressure and 0C, 1 mole of
any gas (i.e. 6.02 x10over23 gas molecules)
occupies approximately 22.4 liters volume.
1 mol gas 22.4 L gas
At STP
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If the proportionality constant is called "R",
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This equation is known as the ideal-gas equation
. An ideal gas is a gas whose physical behavior
is accurately described by the ideal-gas
equation.
Values for the gas constant R Values for the gas constant R
Units Value
L atm/mol K 0.08206
cal/mol K 1.987
J/mol K 8.314
m3 Pa/mol K 8.314
L torr/mol K 62.36
Temperature, T, must always be expressed on an
absolute-temperature scale (K) The quantity of
gas, n, is normally expressed in moles The
units chosen for pressure and volume are
typically atmospheres (atm) and liters (l),
however, other units may be chosen PV can
have the units of energy
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• question what is the pressure exerted by 0.508
  mol O2 in a 15.0L container at 303 K?
• question what is the mass of propane, C3H8 in a
  50.0L container of the gas at STP?

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Molar Mass and Gas Densities
m
m
, n
and
PV nRT
d
M
V
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question calculate the molar mass of a liquid
that vaporized at 100C and 755 Torr yields 185mL
of vapor with a mass 0.523g
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Mixtures of Gases
Daltons law The total pressure of a mixture of
gases equals the sum of the pressures that each
would exert if it were present alone.
Pt is the total pressure of a sample which
contains a mixture of gases P1, P2, P3, etc.
are the partial pressures of the gases in the
mixture
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• Partial pressure
• Each component of a gas mixture exerts a pressure
  that it would exert if it were in the container
  alone.
• The partial pressure of a gas is equal to its
  mole fraction times the total pressure

the term (X1 n1 / nt ) is the mole fraction of
a substance in the gaseous mixture. The mole
fraction of a component expresses the ratio of
the number of moles of one component to the total
number of moles in the mixture.
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question A gaseous mixture made from 10 g of
oxygen and 15 g of methane is placed in a 10.0 L
vessel at 25C. What is the partial pressure of
each gas, and what is the total pressure in the
vessel? question the main component of dry
air by volume N2 78.08, O2 20.95 Ar 0.93 and
CO2 0.04. what are the partial pressures of each
of the four gases in a sample of air at 1.00atm.
question the total pressure of a gas
mixture which containing 0.2 mol of CH4, 0.3 mol
of N2 and 0.5 mol of H2, is 2atm. Calculate
the partial pressures of each gases in atm.
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• Question the reaction of aluminum with HCl
  produces Hydrogen gas,
• Al (s) HCl (aq) ? AlCl3 (aq) H2 (g)
• if 35.5ml of H2 is collected over water at 26 C
  and barometric pressure of 755.0mmHg, how many
  moles of HCl must have been consumed Pwater at
  26 C is 25.2mmHg

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0,37gr KClO3 was heated and O2 produced in this
reaction wwas collected over water. The
temperatuer of water is 23C ve atmosferic
pressure is 751mmHg. What is the volume of O2
collected over water. Vapor pressure of water at
23C is 21,1mmHg
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P tot P gas P H2O
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Kinetic Molecular Theory

• Particles are point masses in constant, random,
  straight line motion.
• Particles are separated by great distances. the
  actual volume of molecules is negligible.
• Collisions are rapid and elastic.
• No force between particles.
• Total energy remains constant.
• The average kinetic energy of the molecules is
  proportional to absolute temperature

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• Translational kinetic energy,
• Frequency of collisions,
• Impulse or momentum transfer,
• Pressure proportional to impulse times frequency

• Three dimensional systems lead to

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Molecular Speed The root mean square speed
urms
Units for R must be 8.314 joule mol/K for M must
be in kg
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question determine the urms of O2 and H2 at 0?C.
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Diffusion is the process of the mixing of gases
with one another. Each gas spreads throughout the
mixture until its partial pressure is the same
everywhere
Effusion is a process in which a gas escapes from
its container through a tiny hole.
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At a given temperature, the rates of effusion of
a gas molecules are inversely proportional to the
square roots of their molar masses. Effusion
time and rates are inversely related.
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question if an unknown gas has a effusion rate
0.468 times the rate of O2 at the same
temperature, what is the molecular weight of the
unknown gas?
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Nonideal (Real ) gases

• An ideal gas is a gas in which the volumes of the
  molecules, intermolecular attractive forces and
  the loss of kinetic energy in collisions are
  neglected.
• Compressibility factor PV/nRT1 for ideal
  gases.
• Gases tend to behave ideally at high temperatures
  and low pressures, and tend to behave nonideally
  at low temperatures and high pressures.

Deviations occur for real gases. PV/nRT gt 1 -
molecular volume is significant. PV/nRT lt 1 -
intermolecular forces of attraction.
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Substance a (L2 atm/mol2) b(L/mol)
He 0.0341 0.0237
H2 0.244 0.0266
O2 1.36 0.0318
H2O 5.46 0.0305
CCl4 20.4 0.1383