Gases
Recall the states of matter:
· solid: molecules rigidly bonded (definite shape & volume)
· liquid: molecules bonded (definite volume), but loosely. Bonds continually breaking & re-forming (indefinite shape)
· gas: molecules not bonded (indefinite volume & shape)
· plasma: heat of surroundings > ionization energy, so electrons are loosely bonded & continually dissociate from and re-associate with ions. Electrical charge is fluid and in continual motion.
evaporation: conversion of liquid to gas.
boiling point: temperature at which a liquid completely evaporates.
normal boiling point: the boiling point of a liquid at a pressure of 1 atm.
Variables
|
Variable |
Units |
Description |
|
n |
moles (mol) |
amount of gas (proportional to # molecules) |
|
V |
liters (L) |
volume = space that gas takes up |
|
T |
Kelvin (K)[*] |
temperature = ability to transfer heat (proportional to kinetic energy of molecules) |
|
P |
mm Hg (torr), atm, kPa, etc. |
pressure = average force on the walls of the container due to collisions of molecules |
Definitions
absolute zero: the temperature at which molecules are moving so slowly that they can’t transfer energy to other molecules. Absolute zero is −273.15°C = 0 K
vacuum: the absence of gas molecules. In a total vacuum, the Pressure = 0
“Standard Pressure” = 1 bar (100. kPa)[†]
“Standard Temperature” = 0oC = 273.15 K
“Room Temperature” = 25oC = 298 K
S.T.P. is “Standard Temperature and Pressure”, which means 0oC and 100 kPa.
1 mole of an ideal gas has a volume of 22.4 L at 0oC and 1 atm of pressure.
Conversion Factors
Pressure Conversions:
1 atm º 101.325 kPa
º 1.01325 bar
º 101,325 
º 101,325 Pa
1 atm º 760 mm Hg º 760 torr = 29.92 in. Hg
1 atm = 14.696 
= 14.696 p.s.i.
Temperature Conversions:
K º oC + 273.15
oF º (1.8 × oC) + 32
oR º oF + 459.67