PHYSICAL
CHARACTERISTICS OF
GASES
Or
GAS LAWS
KINETIC MOLECULAR
THEORY
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1. Ideal gases vs. Real gases
2. Perfect elasticity
3. Average kinetic energy
KE= ½ mv2
Properties of gases
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2.
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6.
Expansion
Fluidity
Low density
Compressibility
Diffusion
Effusion
Pressure
What is it???
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Barometer/Manometer
Millimeters/Torrs
Atmospheres
kiloPascals
1 atm. = 101.3 kPa = 760 mm
7.5 mm = 1 kPa
Conversions
• Change 800 mm to atm. and to
kPa.
• Change 108 kPa’s to mm and
atm.
Practice:
• Convert 699 mm to kPa and
atm.
• Convert 1.05 atm to kPa and
mm.
• Convert 101.9 kPa to mm and
atm
Gases and Temperature
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Kelvin scale 0o Celsius = 273K
Conversion:
Add 273 to Celsius temperature
Change 25oC to Kelvin
Change 287K to Celsius
Convert 45oC to Kelvin
Convert 30 K to Celsius
Boyle’s Law
• Robert Boyle theorized that the
pressure and volume of a gas
were indirectly proportional.
What does this mean??
• PV = k
Problems
• A gas is collected at a constant
temperature of 25o with a
pressure of 689 mm and volume
of 32 mL. Find the pressure if
the volume goes to 55 mL?
• V1 P1 = V 2 P2
One more:
• 45 mL of a gas is collected at
102.7 kPa. Find the volume if
the pressure goes to 705 mm.
Charles’ Law
• Charles worked with
temperature and volume of
gases.
• Temperature and volume are
directly proportional.
• V/T = k
Problems:
V1/ T1 = V2/ T2
• If 28 mL of H2 are collected at 28oC.
What is the volume at 36oC at
constant pressure?
• Kelvin!!!
• If 35 mL of N2 are collected at
31oC,what is the temperature in oC if
the volume rises to 45mL?
Gay –Lussac’s Law
• Gay- Lussac worked with
pressure and temperature of
gases.
• He said that pressure and
temperature were directly
proportional.
• P/T =k
Problems:
• A gas is collected at 43oC and a
pressure of 1.2 atm. Find the
new pressure if the temperature
drops to 21oC. Kelvin!!!
• P1/T1 =P2 /T2
Another problem:
• At constant volume,CO2 is
collected at 768mm with a
temperature of 23oC. Find the
new temperature in oC of 99.1
kPa’s of pressure.
COMBINED GAS LAW
• PUT THE THREE EQUATINS
TOGETHER AND MAKE INTO
ONE.
• WRITE THIS EQUATION.
• V1P1/ T1 = V 2P2/ T2
PROBLEMS
• 25 CM3 OF HYDROGEN IS
COLLECTED AT 260C WITH A
PRESSURE OF 1.2 ATM. FIND
THE NEW VOLUME IF THE
PRESSURE DROPS TO .98 ATM
AND THE TEMPERATURE
DROPS TO 220C.
ANOTHER PROBLEM
• 78 cm3 OF OXYGEN IS
COLLECTED AT 42OC WITH A
PRESSURE OF 767mm. FIND
THE NEW VOLUME AT STP.
Combined:
• 35 cm3 of N2 is collected at .98
atm of pressure with a
temperature of 210C. What is
the new temperature in 0C if the
volume rises to 45 cm3 and
pressure rises to 788 mm?
Over water problems
• 15 liters of
Chlorine is
collected over
water at 718 mm
of pressure at a
temperature of
60oC. Find the new
volume at 766 mm.
This is Dalton’s Law of partial
pressure.
The total pressure of a container
with many gases is the sum of the
partial pressures.
ANOTHER PROBLEM:
• 25 mL of Fluorine gas is
collected over water at 25 oC
with a pressure of 102 kPa’s.
Find the new pressure of 32
mL.
REVIEW
• 33 mL of O2 is collected over
water at 40oC at a pressure of
697 mm. Find the new volume at
300C with a new pressure of
1.01 atm.
Another one:
• 65 mL of F2 are collected over
water at 280C with a pressure of
101.8 kPa. Find the new
temperature of the gas at
standard pressure.
For the quiz:
• 50.0 mL of a gas is collected
over water at STP. Find the new
volume if the new pressure is
.97 atm and new temperature is
• 180C.
Ideal gas law
• This is the last gas law and it
involves all variables PLUS the
mass of the gas.
• Variables:
• P= atmospheres
• R=.0821 L. Atm / K. mole
• V=liters
n= moles
• T = Kelvin
THE FORMULA
• PV = n RT
• YOU MUST HAVE THE RIGHT
UNITS TO USE THE CONSTANT!!
EXAMPLES
• What is the volume of H2 gas if
15 grams is collected at 25oC
with a pressure of .89 atm.?
PROBLEM #2
• What is the pressure of 3.5
grams of CO2 that is collected
at 24oC with a volume of 550
mL?
PROBLEM #3
• What is the mass of chlorine
gas,Cl2, if 4.8 liters are
collected over water at 102.7
kPa’s with a temperature of
28oC?
Problem #4
•Find the volume of O2
that is collected over
water at 25oC with a
pressure of 736 mm and
mass of 16 grams.
Molar mass problems
• What is the molar mass of 5.7
grams of a gas at 230C with a
volume of 4.1 liters at 1.1 atm
of pressure?
• Formula:
•M = mRT/PV
•M = molar mass
•m= mass
A problem:
• What is the molar mass of 4
grams of a gas with a pressure
of 791 mm at 42oC with a
volume of 450 mL?
Molar mass:
• What is the molar mass of a
sample of Ar with .0045 moles
that has a pressure of 725 mm
at 210C and a volume of 55 mL.
Molar mass
• What is the molar mass of CO if
6.5 grams occupies 2.5 liters at
21oC with a pressure of 737
mm?
MOLAR VOLUME
PROBLEMS
• To calculate molar volume and
molar mass, you need to know
that:
• 1 mole of any gas occupies 22.4
liters of volume at STP.
PRACTICE:
• What is the molar volume of 35
grams of CO2 at STP?
More molar volume
• What is the number of moles of
H2 at STP if you collect 350 mL?
Molar volume with a
twist:
• How many grams of SO2 gas at
STP occupies 450 millilters of
volume?
Graham’s Law
• The rate of the movement of a
gas is dependent on its mass.
• Which gas will diffuse or effuse
faster?
• N2 or F2 ??
Ideal gas law review
• What is the mass of 68 mL of Ne
with a pressure of 99.7 kPa’s
that is collect OVER WATER at
26oC?
Molar volume review
• How many liters does 18 grams
of Cl2 occupy at STP?