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