# Ideal Gases

As a beginning it is helpful to recall some aspects of dealing with gases and vapors.

Most Gases and vapors in CVD are for practical purposes "ideal":

PV = NRT

P = pressure (Pascal)

V = volume (m3)

N = number of (gram)moles

R = universal gas constant, 8.3 Joules/mole K

T = absolute temperature (K)

Gas flows are usually measured and reported as:

standard liters per minute (SLPM) or
standard cubic centimeters per minute (sccm).

Both measure gas volume at 0 C, 1 atmosphere: these are measures of MOLAR flow

Pressure is often also reported in other units, most frequently Torr (which are millimeters of mercury), and standard atmospheres.

## USEFUL CONVERSIONS:

1 atm = 760 Torr = 101,000 Pa
1 Pa = 7.6 milliT = 7.6 mT
1 cubic meter = 1000 liters = 106 cm3
K = C + 273
1 mole = 22.4 liters at "STP" (0 C, 1 atmosphere)
1 liter = 0.045 moles at STP
1 cm3 = 4.5x10-5 moles @ STP
1 cm3 = 6.4x10-8 moles @ 1 Torr, 23 C
1 A/minute = 1.6E-10*(molar density)
moles/(cm2 second)
1 SLPM = 7.4x10-4 moles/second
1 sccm = 7.4x10-7 moles/second

k = 1.38E-23 J/°C