chem chapter 5

• made up of all nonmetals
• low MW compounds
• expand to fill a container
• gases are compressible
• gases mix homogeneously when combined

gas of a compound that is liquid at the given temperature

increase in pressure because of more gas molecs colliding with the walls

• gases in atmosphere are "pulled" toward earth by gravity --- causing pressure
• how is it measured?
• barometer
• usually measured in atm

how atmosphere is measured

• standard atmospheric pressure
• enough pressure to push mercury(Hg) column to a height of 760mmHg = 760 torr

1atm = 760mmHg = 760 torr

manometer

• *units have to be the same for P_gas & P_atm
• delta(h) = difference in heights

if column heights are equal: P_gas = P_atm

if P_atm > Pgas P_gas = P_atm - delta(h)

if P_atm < P_gas P_gas = P_atm + delta(h)

• *atmospheric pressure does not matter
• vacuum is on "open" end
• vacuum:
• absence of any molecs
• 0 pressure
• Gas must push harder than vacuum to have pressure
• P_gas = delta(h)

• T = temp, must be in Kelvin(K)
• P = pressure
• V = volume
• n = # of moles of gas present
• (never a gram relationship)

PV=nRT

R, ideal gas constant...use block!! or 0.08206L*atm/mol*K

• 22.4L*1atm
• 1mol*273K

1atm = 760mmHg(or torr) = 101.3kpa

• P₁V₁ = P₂V₂
• V goes up, P goes down

• V₁/T₁ = V₂/T₂
• V goes up, P goes up

• V₁/n₁ = V₂/n₂
• V goes up, n goes up

• while the MW of gases can vary significally, the volume depends only on the number of particles of gas present (moles)
• weights vary (because of MW), but at STP, 1 mole of gas will always have the same volume.

hypothetical gas that behaves according to the ideal gas law (PV= nRT)

mass per unit volume (mass/volume)

• d_gases = g/L
• d_liquids = g/mL

OR

d = P(MW)/ RT

• original:
• d = P(MW)/RT

• rearranged:
• MW = dRT/P

• each gas acts like it's alone
• identity of molecs of gas is not important

the total pressure of a mixture of gases is the sum of the partial pressure of gases in the mixture

P = nRT/V

*pressure depends on the number of molecules/atoms or moles of gas present

a way to visualize what the molecules are doing