# Chem Chapter Five

## Terms

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Atmosphere
the mixture of gases that surrounds the earth's surface
equal volumes of gas at the same temperature contain the same number of particles
Boyle's Law
the volume of a given sample of gas at constant temperature varies inversely with the pressure
Charles' Law
the volume of a given sample of gas at contstnat pressure is directly proportional to the temperature in kelvins
Dalton's Law of Partial Pressures
for a mixure of gases in a container, the total pressure exerted is the sum of the pressures that each gas would exert if it were alone
Diffusion
the mixture of gases
Effusion
the passage of a gas through a tiny orfice into an evacuated chamber
Graham's Law of Effusion
the rate of infusion of gas is inversely proportional to the square root of the mass of the particles
Ideal gas
a gas that obeys the equation, PV=nRT
Ideal Gas Law
an equation of state for a gas, where the state of the gas is its condition at a given time; expressed by PV=nRT, where P=pressure, V= volume, n=moles of gas, R=the universal gas constant, and T=absolute temperature. This eqation expresses the behavior approached by real gases at high T and low P.
Kinetic molecular theory
a model that assumes that an ideal gas is composed of tiny particles (molecules) in constant motion
Manometer
a device used for measuring the pressure of a gas in a container
Millimeters of mercury
(mm Hg) a unit of pressure, also called a torr; 760 mm Hg=760 torr =101,325 Pa = 1 standard atmosphere
Molar volume
the volume of one mole of an ideal gas; equal to 22.4L at STP
Mole fraction
the ratio of the number of moles of a given component in a mixture to the total number of moles in the mixture
Partial pressures
the independent pressures exerted by different gases in a mixture
Root mean square velocity
the square root of the average of the sqaures of the individual velocities of gas particles
Standard atmosphere
a unit of pressure equal to 760mm of Hg
Standard temperature and pressure
the condition of 0 degrees celsius and 1 atm of pressure
Torr
another name for millimeter of mercury (mm Hg)
Universal gas constant
the combined proportionality constant in the ideal gas law; 0.08206 L atm/K mol
gas described quantitatively from four factors
volume, pressure, temperature, and amount of gas present
absolute zero
this temperature where volumes of gas extrapolate to zero
pressure
force per unit area
Pressure is equal to force per unit area. Which of the following equations is dimensionally consistent with this definition? g = m/s2, d = g/cm3, h = height
p = gdh
According to the postulates of the kinetic theory of gases, the size of the molecules that make up the gas is necessary in calculations using the ideal gas law.
false
According to the postulates of the kinetic theory of gases, increasing the volume of a container at constant temperature will result in a decrease in the pressure the gas exerts in the container
true
Problems with the ideal gas law arise as
molecular size and interactions become important at high pressure and low temperature
Which of the following does NOT describe an ideal gas?
strong repulsion between molecules results in ideal gas behavior
Torricelli's original determination of atmospheric pressure
his barometer--a filled tube with Hg and inverted it into a dish filled with Hg
Units used for the measurement of pressure and conversions between them
760mm Hg= 760 torr = 1 atm = 101.3 kPa
Determination of the pressure of an individual gas
use a manometer; gas in flask exerts a pressure (Pgas); atomospheric gases coming into the tube exert a pressure (Patm); opposite directions; opposing forces;
a) atmosphereic pressure > gas pressure: subtract height of Hg difference from atm. pressure
b) Patm < Pgas: add h to atm. pressure
_____________________________
If the tube is closed to the atmosphere and a vacuum is established, the Hg levels in the U-tube will be equal --when a gas is introduced into the flask, the height of the Hg difference will be an actual measurement of the gas pressure
Why mercury
high density; workable substance
Boyle's Law:
1) studied
2) constant
3) relationship between factors
4) formula
1) pressure and volume
2) temperature
3) inverse
4) P1V1=P2V2
Charles' Law:
1) studied
2) constant
3) relationship
4) formula
5) development of the Kelvin temperature scale
1) temperature and volume
2) pressure
3) direct
4) V1/T1 = V2/T2
5) all charles' measurements comaparing T and V for various gases resulted in a straight line graph... when these lines were extrapolated to zero volume they all intersected the x-axis (temperature) at the same point: -273.15 degrees C...working with Lord Kelvin, they identified this value as absolute zero and established the relationship... K= degrees C +273.15
Combined Gas Law
Keep original relationship to volume for P and T and combine all three together:
p1v1/t1 = p2v2/t2
1) studied
2) constant
3) relationship
4) formula
1) volume and moles/particles
2) temperature
3) direct
4) V1/N1 = V2/N2
The derivation of the Ideal Gas Law from the 3 separate gas laws
V=R(Tn/P)
Review Stoichiometery
-Calculation to relate two different substances in a chemical reaction
-Only way to relate two different substances is with mole ratio
-Use molar mass to make conversions (mass<-->mole)
Relationship between the volume of a gas and one mole and the conditions that are necessary
One mole = 22.4L for ANY gas at STP; set value at zero degrees celsius and 1 atm pressure
CALCULATIONS not under STP
* cannot use 22.4L
* use stoichiometry to determine moles of gas
*use ideal gas law equation to determine volume
(or vice versa)
Dalton's Law of Partial Presures
For a mixture of gases in a container, the total pressure exerted is the sum of the pressures that each gas would exert if it were alone.
CALCULATIONS using Partial Pressures & idea of mole fraction
mole fraction: ratio of number of moles at a single component in a miture to total number of moles in the mixture
The statements of KMT
1) volume of the individual particles can assumed to be negligible
2) particles are in constant motion; the collisions of the particles with the walls of the container are the cause of the pressure exerted by the gas
3) the particles are assumed to exert no forces on each other; they are assumed neither to attract nor to repel each other
4) the average kinetic energy of a collecion of gas particles is assumed to be directly proportional to the kelvin temperature of the gas
These statments support the gas laws
1) boyle's
2) gay-lussac's
3) charles'