11/14/2013
IDEAL GAS LAW
Behavior and Properties of Gases

Today:
◦ Composition and Pressure of
the Atmosphere
 Units for measuring pressure
◦
◦
◦
◦

Next Meeting
◦ EXAM 3 Review: Bring
Questions for clarification
Boyle’s Law
Charles’ Law
Gay Lussac Law
Combined Gas Law
◦IDEAL GAS LAW
Concept Check:
Predicting Boiling Points
Which molecule would have the highest boiling point?
A. CH4
B. CO2
C. NH3
D. N2
E. CH3CH2CH3
1
11/14/2013
Example Problems:
•
If the pressure of a confined gas is tripled while its
temperature remains constant, what change will be
observed?
•
At constant temperature, 10.0 L of N2 at 0.983 atm
is compressed to 2.88 L. What is the final pressure
of N2?
•
A sample of gas occupies 175 mL at 22 C and 218
mm Hg. What is the pressure of the gas if the
volume is decreased to 122 mL and the
temperature increased to 75 C?
If Felix started his ascent at 80
oC with a balloon volume of 3.0
x 106 L, what would be the
final volume of his balloon if
his final altitude was 127,852 ft
with a temperature of -8.9 oC
and a pressure of 0.04 psi?
𝑷𝟏 𝑽𝟏
𝑻𝟏
=
𝑷𝟐 𝑽𝟐
𝑻𝟐
2
11/14/2013
Avogadro’s Law:
When all else is constant: the volume of a gas is directly
proportional to the number of moles of the gas
Volume ∝ 𝒏 (# of moles of gas)
𝑽
= Constant
𝒏
𝑽𝟏
𝒏𝟏
The more gas present,
the larger the volume.
𝑽
= 𝒏𝟐
𝟐
Ideal Gas Law:
𝑷𝑽
= 𝑼𝒏𝒊𝒗𝒆𝒓𝒔𝒂𝒍 𝑮𝒂𝒔 𝑪𝒐𝒏𝒔𝒕𝒂𝒏𝒕 (𝑹)
𝒏𝑹𝑻
PV = nRT
3
11/14/2013
Ideal Gas Law:
• R is a constant for all gases. The value of R depends on the units
we use for the various properties.
»
»
»
»
Volume = Liter (L)
Temperature = Kelvin (K)
Number of moles = moles (mol)
Pressure units vary. We commonly use: atm, Pa, kPa, mmHg
R  0.08206
L  atm
L mmHg
L Pa
 62.37
 8314
K mol
K mol
K mol
 8.314
L kPa
J
 8.314
K mol
K mol

Example Problems
• What volume of O2, measured at 18.9 C and
700. torr, is needed for the complete
combustion of 12.1 grams of propene, C3H6?
• Show that the relationship 22.4 L / 1 mol for
gases at STP is consistent with the ideal gas law.
4
11/14/2013
Example Problems
• The pressure in a 10.0 L flask containing only
propane is 0.912 atm at 78 C. How many
moles of propane are in the flask?
• A 50.0 L cylinder of He has a pressure of 151
atm at 298 K. What mass of He is inside the
cylinder?
5