Gas

Gases ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],James K Hardy

Elemental states at 25 o C He Rn Xe I Kr Br Se Ar Cl S Ne F O P N C H Li Na Cs Rb K Tl Hg Au Hf Ls Ba Fr Pt Ir Os Re W Ta Po Bi Pb Be Mg Sr Ca Cd Ag Zr Y Pd Rh Ru Tc Mo Nb Ac Ra Zn Cu Ti Sc Ni Co Fe Mn Cr V In Sb Sn Ga Ge Al Gd Cm Tb Bk Sm Pu Eu Am Nd U Pm Np Ce Th Pr Pa Yb No Lu Lr Er Fm Tm Md Dy Cf Ho Es At Te As Si B 5 - 2 Solid Liquid Gas

Observed properties of matter ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

The gaseous state ,[object Object],[object Object],[object Object],[object Object],[object Object]

Gas pressure ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],force area

Barometer Device used to measure atmospheric pressure. One atm 760 mm Hg 29.9 in Hg vacuum

The gas laws ,[object Object],[object Object],[object Object]

Units we will be using ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Gas laws ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Boyle’s law ,[object Object],[object Object],[object Object],[object Object],[object Object]

Boyle’s law Increasing the pressure on a sample on gas decreases it volume at constant temperature. Note the effect here as weight is added.

Charles’ law The volume of a gas is directly proportional to the absolute temperature (K). V T = k or V 1 V 2 T 1 T 2 Pressure and number of moles must be held constant! =

Charles’ law When you heat a sample of a gas, its volume increases. The pressure and number of moles must be held constant.

Charles’ Law Placing an air filled balloon near liquid nitrogen (77 K) will cause the volume to be reduced. Pressure and the number of moles are constant.

Gay-Lussac’s Law ,[object Object],[object Object],[object Object]

Gay-Lussac’s Law ,[object Object],[object Object],[object Object],[object Object],[object Object],+ H 2 H 2 O 2 H 2 O H 2 O

Avogadro’s law ,[object Object],[object Object],[object Object],[object Object],=

Avogadro’s law If you have more moles of a gas, it takes up more space at the same temperature and pressure.

Standard conditions (STP) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

The ideal gas law ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Example ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Ideal gas law PV nT ( 1 atm ) ( 22.4 L ) ( 1 mol ) ( 273.15 K) R = = 0.08206 atm L mol -1 K -1 R = R can be determined from standard conditions.

Ideal gas law ,[object Object],[object Object],[object Object],[object Object],[object Object]

Ideal gas law P 1 V 1 n 1 T 1 = R = P 2 V 2 n 2 T 2 This one equation says it all. Anything held constant will “ cancels out” of the equation

Ideal gas law Example - if n and T are held constant P 1 V 1 n 1 T 1 = P 2 V 2 n 2 T 2 ,[object Object],[object Object],Boyle’s Law

Example If a gas has a volume of 3.0 liters at 250 K, what volume will it have at 450 K ? P 1 V 1 n 1 T 1 = P 2 V 2 n 2 T 2 V 1 T 1 = V 2 T 2 Cancel P and n They don’t change We end up with Charles’ Law

Example If a gas has a volume of 3.0 liters at 250 K, what volume will it have at 450 K ? ,[object Object],[object Object],[object Object],P 1 V 1 n 1 T 1 = P 2 V 2 n 2 T 2 V 1 T 1 = V 2 T 2

Dalton’s law of partial pressures ,[object Object],[object Object],[object Object],[object Object]

Partial pressure example ,[object Object],[object Object],[object Object]

Partial pressure example ,[object Object],[object Object],[object Object],(1.0 atm) (46 l) (0.08206 l atm K -1 mol -1 )(298.15K) (1.0 atm) (12 l) (0.08206 l atm K -1 mol -1 )(298.15K)

Partial pressure example ,[object Object],[object Object],[object Object],[object Object],(1.9 mol) (298.15 K) (0.08206 l atm K -1 mol -1 ) (5.0 l) (0.49 mol) (298.15 K) (0.08206 l atm K -1 mol -1 ) (5.0 l)

[object Object],[object Object],Graham’s law Rate A MM B Rate B MM A =

Diffusion and effusion ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Kinetic-molecular theory ,[object Object],[object Object],[object Object],[object Object]

Kinetic-molecular theory ,[object Object],[object Object],[object Object],[object Object],[object Object],1 2

Kinetic-molecular theory O 2 at 25 o C O 2 at 700 o C H 2 at 25 o C Average speed Fraction having each speed 0 500 1000 1500 2000 2500 3000 Molecular speed (m/s)

Real gases We can plot the compressibility factor ( PV/nRT ) for gases. If the gas is ideal, it should always give a value of 1. Obviously, none of these gases are ‘ideal.’ Compressibility factor 0 5 10 Pressure, atm H 2 N 2 CH 4 C 2 H 4 NH 3

Real gases ,[object Object],[object Object],[object Object],[object Object],[object Object]

Van der Waals equation ,[object Object],Correction for Molecular volume Correction for attractive forces between molecules P + an 2 V 2 ( V - nb ) = nRT ( )

Van der Waals constants ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Gas

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