Chpt 5 - Gases• Gas Law Development• Dalton’s Partial pressure law• Graham’s effusion• Kinetic Theory

–Root-mean-square velocity

• van der Waals equation of state• HW: Chpt 5 - pg 119-128, #s 5, 22, 23, 25, 31,

32, 35, 39, 41, 46, 55, 64, 66, 71, 75, 77, 81, 91, 95, 97, 101, 124 Due Mon 9/28

Torricelli barometer

The height in mm of mercuryabove the surface of the resevoirof mercury determines the pressure.The units are mmHg.

mmHg is also the same unit asTorr. i.e. standard pressure is 760 mmHg and 760 Torr

Pressure is? Units?

Simple Manometer

Similar to the barometer, the height difference of the Hg relates the pressure difference in the unknown gas bulb side to the current atmospheric pressure.

The higher Hg side has the _____ pressure. (higher/lower)

Boyle’s Law

• Constant temperature experiments demonstrated the PV=constant graphing this yields an inverse relationship

• Thus if the pressure of volume changes at a constant temperature

P1V1 = P2V2

Charles’s Law

• Constant pressure experiments demonstrated that Volume is directly proportional to Temperature (Kelvin)

V1 = V2

T1 T2

• Several gases were used & all extrapolate to zero volume and the same temperature at negative 273oC

Plots of V vs. T(ºC)

Charles’s Law Experiment results

Combined Gas Law

P1V1 = P2V2

T1 T2

Avogadro’s Law - equal volumes of gas contain equal particles of gas

V = k n

At constant temperature and pressure the volume is directly proportional to the number of moles of gas.

Ideal Gas Law

• Putting it all together, we can calculate that constant now. The universal gas constant R.

PV=R or PV=nRT

nT R =0.0821 l *atm/mol*K

=8.31 l *kpa/mol*K

Effusion of Gas into Evacuated Chamber

If more than one type of gas or more than one isotope, which gas effuses faster?

Lighter gas movesFaster!!

KE = 1/2 mv2

Relative Molecular Speed Distribution of H2 and UF6

Diffusion Rates of NH3 and HCl Molecules Through Air

Plots of PV/nRT vs. P for Several Gases

Plot of PV/nRT vs. P for N2 Gas

Plot of PV vs. P for Several Gases

Values of the van der Waals Constants for Common Gases