Ideal Gas Law
What is the Ideal Gas Law?
An ideal gas is defined as one in which all
collisions between atoms or molecules are
perfectly elastic and in which there are no
intermolecular attractive forces. In such a gas,
all the internal energy is in the form of kinetic
energy and any change in internal energy is
accompanied by a change in temperature.
Measurements necessary to accurately
describe a sample of gas:
An ideal gas can be characterized by four
variables:
• pressure
• volume
• temperature
• number of moles
Mathematical Expression
PV = nRT
P = pressure
V = volume
T = temperature
n = number of moles
R = gas constant
(R = 0.0821 if P = atm, V = L, and T = K)
(R = 8.314 if P = Pa, V = m3, and T = K)
Practice Problems
1.What volume would be occupied by 100g
of oxygen gas (O2) at a pressure of 1.5
atm and a temperature of 25°C?
P=
V=
n=
R=
T=
2. A balloon is inflated with 0.2495g of
helium (He) to a pressure of 1.26 atm. If
the desired volume of the balloon is 1.25L,
what must the temperature be?
P=
V=
n=
R=
T=
3. A welder’s acetylene tank has a volume
of 75m3. It is stored at a temperature of
23.24°C and a pressure of 76,670Pa.
How many moles of acetylene are in the
tank?
P=
V=
n=
R=
T=
4. A sample of bromine gas (Br2) is loaded
into an evacuated demonstration bottle at
STP (1atm and 273K). The volume of the
bottle is 0.25L. How many moles of Br2
will be contained in the bottle?
P=
V=
n=
R=
T=
Dalton’s Law of Partial
Pressures
The sum of the partial pressures of all the
components in a gas mixture is equal to the
total pressure of the gas mixture.
PT = Pa + Pb + Pc ……
Practice Problems
1. What is the pressure of a mixture of
helium, nitrogen, and oxygen if their
partial pressures are 600, 150, and 102
mmHg respectively?
2. Flask contains a mixture of hydrogen gas
and oxygen gas. The pressure being
exerted by these gases is 785 mmHg, as
determined by a manometer. If the partial
pressure of hydrogen gas in the mixture
is 395 mmHg, what is the partial pressure
of the oxygen gas?
3. What is the atmospheric pressure of the
partial pressures of nitrogen, oxygen, and
argon are 77.75 kPa, 9.94 kPa, and 1.99
kPa, respectively?