IDEAL GAS
LAW
What’s the Diff?!
• What is the difference
between a real gas and an
ideal gas?! Google it! Or read
page 172 in your textbook!
Ideal Gas
• Molecules size is negligable
• Gas molecules are in constant, random,
stratight line motion because…
• …no force exist between them
• Gas molecules undergo perfectly elastic
collisions, where no energy is lost, collisions
happen quickly
Real Gas
• In high pressures molecules are forced
together and so the size is greater than the
space between the molecules
• As temp decreases, molecules slow down and
may eventually stick together and become
liquid
• Molecules aer more like soft spheres and can
change shape durig a collision and rebound
making this process a little slower
• Boyle’s Law = volume of gas is
inversely proportional to the pressure
• Charles’ Law = the volume of a gas is
directly proportional to the absolute
temperature
• Avogadro’s theory = the volume of a
gas is directly proportional to the
chemical amount of matter
Ideal Gas Law
PV = nRT
• The ideal gas law is a
combination of Charles’ Law,
Boyles’ Law and Avogadro’s
Hypothesis
• Boyle’s Law = PV = a constant
• Charles’ Law = P/T = a
constant
• Avogadro’s theory = V/n = a
constant
All together now
• PV = R (universal gas constant)
nT
• R = 8.31 L kPa / mol K
So…
PV = nRT
Example:
• What is the volume of 3.35mol of neon at 42.5
degrees Celsius and 96.5kPa?
•
•
•
•
•
List your knowns
T = 42.05C = 315.5K
R = 8.31LkPa/molK
n = 3.35mol
P = 96.5kPa
List your unknowns
V = ????
PV = nRT
• V = nRT / P (rearranged to solve for unknown)
• V = 3.35mol x 8.31LkPa/molK x 315.5K
96.5kPa
• V = 91.0L
Example 2:
• What is the volume of 66.4g of CO2(g) at
32.0C and 115kPa?
•
•
•
•
•
Knowns
g = 66.4g
T = 32.0C = 305K
P = 115kPa
R = 8.31LkPa/molK
Unknowns
n = mols?????
V = ??????
Example 3
• What is the molar mass of 3.827g of gas at a
temperature of 25C, 11.38L and 2.88atm?