Ideal Gas Law Chapter 14.3
Jan 19, 2016
Ideal Gas Law
Chapter 14.3
Ideal Gas Law
• The ideal gas law combines:– pressure– temperature– volume– # of particles (amount)
Increasing Amount of Particles
• If the amount of gas particles increases:– the pressure will increase OR– the volume will increase
Effects of increased numbers of particles
• Since P1V1 = P2V2
T1 T2
PV = k
T
stays constant as long as the number of particles stays the same
Effects of increased numbers of particles
PV = k
T
• k varies with the amount of gas particles (n)
• k = nR
• R was determined experimentally
• R is called the ideal gas constant
Vocabulary Word
• ideal gas law: describes the physical behavior of an ideal gas in terms of the temperature, volume and pressure and the number of moles of a gas that are present
• PV = nRT
Ideal Gas Constant
• R has different numerical values depending on the unit for pressure:– Patm R = 0.0821
– PkPa R = 8.314
– PmmHg R = 62.4
Units for the Ideal Gas Law
• Volume (liters)
• Temp (Kelvin)
• n (moles)
Properties of Ideal Gases
• the gas particles have no intermolecular forces of attraction or repulsion
• in the real world gas particles DO have a small but measurable volume
Real Gases
• most gases behave like ideal gases at many temperatures and pressures
• we can use the ideal gas law to get a very close approximation of experimentally verified values
Real Gases
• at extremely high pressures or low temperature intermolecular forces become important
• this allows gases to liquify
Intermolecular Forces• size and geometry
(shape) can increase the intermolecular forces of attraction,
• values calculated with the ideal gas law will be off– polar gases (water
vapor)
– larger gases (butane)
Using the ideal gas law to calculate moles (n)
• when any 3 values are given, the 4th value can be calculated
• If P = 3.18 atm and V = 0.044L at 25oC, how many moles of gas are present?
P = 3.18 V = 0.044 T = 25 + 273 = 298
Using the ideal gas law to calculate moles (n)
P = 3.18 V = 0.044 T = 25 + 273 = 298
PV = nRT
(3.18) (0.044) = n (0.0821) (298)
Using the ideal gas law to calculate moles (n)
(3.18) (0.044) = n (0.0821) (298)
(3.18) (0.044) = n
(0.0821) (298)
6.9 x 10-3 mol = n
Using the ideal gas law to calculate temperature
n = 2.49 mol
V = 1L
P = 143 kPa
T = ?
(143) (1) = (2.49) (8.314) Tk
Using the ideal gas law to calculate temperature
(143) (1) = (2.49) (8.314) Tk
(143) (1) = Tk
(2.49) (8.314)
6.91 = Tk
- 266o = oC
Using the ideal gas law to calculate volume
• n = 0.323 mol
• T= 265K
• P = 0.900 atm
(0.900) V = (0.323) (0.0821) (265)
V = (0.323) (0.0821) (265) = 7.821 L
(0.900)
Using the ideal gas law to molar mass
• The ideal gas law can be used to determine the molar mass of a gas
• moles of a gas = mass of the gas
molar mass
• PV = nRT becomes PV = mRT
M
PV = mRT
M
solve for M, and M = mRT
PV