Pressure and Phase Relationships

Ch. 13 States of Matter

Fahrenheit, Celsius and Kelvin• Fahrenheit based on

reference temperatures of brine solution at 0 and in mouth at 96 or wife’s armit

• Celsius based on freezing pt and boiling point of water] F = 1.8C + 32

• Kelvin based upon absolute zero and no negative values K = C + 273

Pressure

• Pressure: Defined as force per unit area caused by gas molecules colliding with surface

• P = F/A• 1 Pa = 1 N/m2

Temperature: defined as a measure of the AVERAGE kinetic energy of a substance (this means that some molecules are moving faster than average and some slower than average)

Liquid-Vapor EquilibriumThe temperature and pressure at which equal amounts of high energy liquid molecules A are escaping to become vapor and vapor molecules B are being slowed down and trapped at surface to return to liquid

Barometer (or manometer) measures pressure

• SI unit is the pascal (1 Pa = 1 N/m2) or kilopascal kPa

• Meteorologists (weather) like mmHg, the height the atmospheres pressure pushes a liquid column upward (more dense liquids don’t get pushed as high and Hg is very dense)

• mmHg are also called Torrs, so 1mmHg = 1Torr

Gas molecules in the atmosphere

• A standard atmosphere (atm) of pressure is defined as

typical air pressure at earth mean sea level

Pressure conversions

• This means 760mmHg = 14.7psi and 101.3kPa = 760 Torr as well

1 atmosphere is a measure of the normal pressure at sea level

1 atm = 101.3kPa = 101,300 Pa = 760 mmHg = 760 Torr = 14.7 psi

A typical atmospheric pressure in Fort Collins CO might be 690 mmHg. Convert this to atmospheres of pressure.

690mmHg x 1 atm = 0.91 atm

760mmHg

Convert the same pressure above into both psi and Torr

13.3 psi and 690 Torr

Phase Diagram of Water