1. Gas Laws, Molecular Weight & Density

2. Ideal Gas Law ...Revisited
Substitute for n
n = mass/M
M = molar mass
PV = nRT
PV =
mass RT M
Rearrange...
mass V
= D
PM =
mass RT V
But....
(Density)
Density
Molar Mass
Temp (K)
Pressure
D = PM RT
PM =
DRT

3. Density: Hot Air Balloons
Graphics:

4. Balloon heated air Density T=120.0 C (393.15K)
More Balloons...
Mair= 28.8 g/mol (Average)
Balloon heated air Density T=120.0 C (393.15K)
D = PM RT =
0.980 atm 28.8g/mol
(L atm)/(mol K)(393.15K)
D = g/L
Surrounding air Density
Density Balloon < Densityair
D = 1.13 g/L
D = g/L
T = 30.2 C (303.35K)
Patm=744.8 torr (0.980 atm)
D = PM RT =
0.980 atm 28.8g/mol
(L atm)/(mol K)(303.35K)
D = 1.13 g/L

5. Balloon heated air Density T=120.0 C (393.15K)
More Balloons...
Mair= 28.8 g/mol (Average)
Balloon heated air Density T=120.0 C (393.15K)
D = PM RT =
0.980 atm 28.8g/mol
(L atm)/(mol K)(393.15K)
D = g/L
Surrounding air Density
Density Balloon < Densityair
D = 1.13 g/L
D = g/L
T = 30.2 C (303.35K)
Patm=744.8 torr (0.980 atm)
D = PM RT =
0.980 atm 28.8g/mol
(L atm)/(mol K)(303.35K)
D = 1.13 g/L