Gases

GASES
OBJECTIVES
To understand pressure and to familiarize the units of pressure
To know and apply the gas laws to determine pressure, volume, and
temperature of a gas
To apply stoichiometry to determine the amounts of gaseous reactants

and products
To explain the gas laws through the kinetic molecular theory of gases
PRESSURE
UNITS OF PRESSURE
PRESSURE
What is a gas?
PRESSURE
What is pressure?
PRESSURE
Pressure – a force that is exerted by the
gas
𝒇𝒐𝒓𝒄𝒆 ( 𝑭 )
𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆( 𝑷 )=
𝒂𝒓𝒆𝒂 ( 𝑨)
PRESSURE
Pressure – a force that is exerted by the
gas
UNITS OF PRESSURE
Atmospheric Pressure (atm)

– the exerted pressure of Earth’s atmosphere
 commonly measured using a barometer
 1 atm is the standard atm.
UNITS OF PRESSURE
1 atm = 760 mmHg

1 mmHg = 1 torr
1 atm = 760 torr
1 atm = 101,325 Pa
1 atm = 1.013 bar
UNITS OF PRESSURE
1 atm = 760 mmHg
Example: 1 mmHg = 1 torr
1 atm = 760 torr
1 atm = 101,325 Pa
1. Convert 923 torr to atm. 1 atm = 1.013 bar
2. Convert 235,648 Pa to torr.

GAS LAWS
BOYLE’S LAW
CHARLE’S LAW
GAY-LUSSAC’S LAW
IDEAL GAS LAW
DALTON’S LAW OF PARTIAL PRESSURE
BOYLE’S LAW
 Robert Boyle
 Pressure is inversely proportional to the volume of a gas
at constant temperature.
P1 V1 = P2 V2
BOYLE’S LAW
BOYLE’S LAW
If a gas occupies 3.60 liters with a pressure of 1.00 atm,
what will be its volume at a pressure of 2.50 atm?
BOYLE’S LAW
A gas occupies 12.3 liters at a pressure of 0.053 atm.
What is the pressure when the volume is decreased to
6150 milliliters?
CHARLES’ LAW
 Jacques Alexandre Cesar Charles
 A volume of a fixed amount of gas is directly
proportional to its absolute temperature at a constant
pressure
CHARLES’ LAW
CHARLES’ LAW
What is the temperature of a 150 L gas, if its original
volume was 300 L at 400 Kelvin?
GAY-LUSSAC’S LAW
 Joseph Gay-Lussac
 also known as Amonton’s Law of Pressure-Temperature
 The pressure of a gas of fixed mass and fixed volume is
directly proportional to the absolute temperature of a
gas
GAY-LUSSAC’S LAW
GAY-LUSSAC’S LAW
A gas has a pressure of 0.370 atm at 323 K. What is the
pressure at 298 K?
AVOGADRO’S LAW
 volume-amount relationship of gas
 The volume is directly proportional to the amount/moles
of gas at constant temperature and pressure.
AVOGADRO’S LAW
AVOGADRO’S LAW
6.2 liters of an ideal gas has 0.73 mole. How many moles
of this gas are present if 1.8 liters of the same gas is
added?
IDEAL GAS LAW
 the equation of state of a hypothetical ideal gas.
 the combination of all the gas laws.
PV = nRT
IDEAL GAS LAW
At what temperature in °C will 0.654 moles of neon gas
occupy 12.30 liters at 1.95 atmosphere?
DALTON’S LAW OF PARTIAL
PRESSURE
 The total pressure exerted by a mixture of gases is the
sum of partial pressure of each individual gas present.
Ptotal = PA + PB + Pc +…
PA = XA Ptotal
PRESSURE
PRESSURE
A mixture of gases contains 4.46 moles of neon (Ne), 0.74
mole of argon (Ar), and 2.15 moles of xenon (Xe).
Calculate the partial pressures of the gases if the total
pressure is 2.00 atm at a certain temperature.
A mixture of gases contains 4.46 moles of neon (Ne), 0.74 mole of argon (Ar), and 2.15 moles of xenon (Xe). Calculate the
partial pressures of the gases if the total pressure is 2.00 atm at a certain temperature.
PRESSURE
24 L of nitrogen gas at 2 atm and 2.0 L of oxygen gas at 2
atm are added to 10 L container at 273 K. Find the total
pressure then find the partial pressure of nitrogen and
oxygen.
24 L of nitrogen gas at 2 atm and 2.0 L of oxygen gas at 2 atm are added to 10 L container at 273 K. Find the total pressure
then find the partial pressure of nitrogen and oxygen.
GAS
STOICHIOMETRY
MASS-VOLUME
VOLUME-VOLUME
MOLE-VOLUME
GAS STOICHIOMETRY
How many liters of NH3 can be produced at a temperature
at 27 degrees Celsius and a pressure of 760 torr, if 20
moles of N2 are consumed?
N2 (g) + 3H2 (g)  2NH3 (g)

How many liters of NH3 can be produced at a temperature at 27 degrees Celsius and a pressure of 760 torr, if 20 moles of N 2
are consumed?
N2 (g) + 3H2 (g)  2NH3 (g)
GAS STOICHIOMETRY
How many liters of H2 will be required at a temperature of
300 K and 3 atm to consume 56 grams of N2?
N2 (g) + 3H2 (g)  2NH3 (g)

How many liters of H2 will be required at a temperature of 300 K and 3 atm to consume 56 grams of N 2?
N2 (g) + 3H2 (g)  2NH3 (g)
GAS STOICHIOMETRY
How many liters of water vapor can be produced if 40
liters of H2 is consumed in the chemical reaction below at
standard temperature and pressure?
2H2 (g) + O2 (g)  2H2O (g)

How many liters of water vapor can be produced if 40 liters of H2 is consumed in the chemical reaction below at standard
temperature and pressure?
2H2 (g) + O2 (g)  2H2O (g)
KINETIC
MOLECULAR
THEORY
KINETIC MOLECULAR THEORY
- Ludwig Boltzmann and Clerk Maxwell
Assumption #1
A gas is composed of molecules considered as “points”,
that are separated from each other by distances far greater
than their own dimensions. Gas molecules possess mass
but have negligible volume.
Assumption #2
Gas molecules are in constant random directions, and they
frequently collide with one another. Collisions among
molecules are perfectly elastic.
Assumption #3
Gas molecules exert neither attractive nor repulsive force
on one another.
Assumption #4
The average kinetic energy of the molecules is
proportional to the temperature of the gas. Any two gases
at the same temperature will have the same average
kinetic energy.
GASES

Gases - P. Poloniae

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To apply stoichiometry to determine the amounts of gaseous reactants

Atmospheric Pressure (atm)

1 atm = 760 mmHg

2. Convert 235,648 Pa to torr.

N2 (g) + 3H2 (g)  2NH3 (g)

N2 (g) + 3H2 (g)  2NH3 (g)

2H2 (g) + O2 (g)  2H2O (g)

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