Gas State Introduction

Gas State

The kinetic-molecular theory of gases can be stated as five postulates:

  • A gas consists of molecules in constant random motion.
  • Gas molecules influence each other only by collision.
  • There are no inter molecular forces of attraction.
  • All collisions between gas molecules are perfectly elastic; all kinetic energy is conserved.
  • The volume actually occupied by the molecules of a gas is negligibly small; the vast majority of the volume of the gas is empty space through which the gas molecules are moving.

Equations of State for Gases

Standard state:

STP Standard temperature and pressure

  • Temperature = 0o C or 273.14 K
  • Pressure = 101.325 kPa
  • Volume = 22.4 L

SATP Standard ambient temperature and pressure

  • Temperature = 25oC or 298 K
  • Pressure = 100 kPa
  • Volume = 24.8 L

Universal Gas Constant

R =  8.314  J/mol K

R =  8.314  kPa dm3/mol K

Commonly used units of pressure

  • Atmosphere written as atm.
  • Kilopascal kPa Conversion unit = clip_image002at STP
  • Torricelli Torr. Conversion unit = clip_image004 at STP
  • Millimeter mm Conversion unit = clip_image006 at STP
  • 1 mm of Hg = 1 torr
  • 1 atm. = 101.325 kPa = 760 torr = 760 mm of Hg = 76 cms of Hg

Temperature

  • Celsius and Kelvin
  • Conversion:
  • Kelvin = degrees Celsius + 273
  • K = oC + 273
  • In all SI metric calculations use only Kelvin values.