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UnitConv

Gas calculations


The gases window

Gas calculation dialogue You may enter values for the temperature of the gas, the pressure of the gas, the size of the molecule, and the relative molar mass into the appropriate icons and then click on Calculate. Pressing RETURN will be the same as clicking Calculate. Use TAB or the up/down arrow keys to move to each writable icon in turn.

If you have entered values for all four parameters, then the following values will be calculated.

The program tries to be intelligent about what to calculate. For example, the velocities require only the temperature and the molar mass to be entered, whereas the mean free path calculation requires temperature, pressure, and size of molecule. The program calculates what it can, and leaves the result fields blank if there is insufficient input data for that calculation. Temperature is always entered as kelvin. If a temperature is not entered, then an error message is generated. Menu buttons are provided in this window to allow you to change the default units used for pressure (atmosphere, N/m2, and torr) and size (pm, nm, and m), and to enter the size either as the diameter of the molecule, or as the cross sectional area. If you choose to enter the size as a diameter, the program assumes the molecule is spherical. We are dealing with the collision cross-section, which is effectively PI x diameter2, since the distance between centres of colliding molecules (of the same type) is 2 x radius.

Some Useful Data

Collision cross-sections/(nm)2 for a selection of molecules

He 0.21 Cl2 0.93
Ne 0.24 CO2 0.52
Ar 0.36 SO2 0.58
H2 0.27 CH4 0.46
N2 0.43 C2H4 0.64
O2 0.40 C6H6 0.88


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UnitConv is © Chris Johnson, 2012
Email:chris@chris-johnson.org.uk