Topic: Pressure (and Partial Pressure)

Do Now: Convert the following units of pressure

249 torr to atm

10432 Pa to kPa

2534 kPa to mmHg

What causes the pressure of a gas in a closed container?

Impacts of gas molecules with walls of container

•Pressure depends on:– # impacts per

unit time– Force each

impactMicroscopic View

Light molecules move faster and hit walls more often

Heavy molecules hit walls with greater force

These 2 effects essentially balance out

**Gas pressure doesn‘t depend on the identity(light like He(g) or heavy like CO2(g))

of the gas**

Molecular Speeds at 298 K•H2 1.93 X 105

cm/sec•He 1.36 X 105 cm/sec

•O2 4.82 X 104 cm/sec *

•Ar 4.31 X 104 cm/sec

•Xe 2.38 X 104 cm/sec

48200 cm 1 in 1 ft 1 mile 3600 sec = se

c2.54 cm

12 in 5280 ft 1 hour

1080 miles per hour

Dalton’s Law of Partial Pressure

• The sum of individual pressures of all the gasses that make up a mixture is equal to the total pressure of the mixture

• PT = P1 + P2 + P3 +…

1 atm = Pressure of N2 + Pressure of O2 + pressure of Ar + pressure of H2) (g) + ……..

In order to figure Partial Pressure of N2 = 1 atm (.7655) = .7655atm