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the Ideal Gas model

One can visualize an ideal gas as one in which there are no intermolecular forces, like a series of perfectly hard spheres which collide but which otherwise do not interact with each other.


In other words, the following conditions are assumed for an Ideal Gas:


• The molecules are perfectly elastic

• The molecules have no size


The ideal gas law has four parameters and a constant, R:


P V = n R T




p is the pressure

V is the volume occupied by  "n" number of moles

n is the number of moles: the amount of gas (see here)

R is the gas constant (with Ideal Gas, R has the same value for all  gases: with volume in liters, KPA pressure and temperature in ° K,  R = 8,314472. The value of R can be determined experimentally with a known amount (number of moles) of gas,  pressure, temperature and volume: R = PV / nT)

T is the temperature


According to the Ideal Gas law let’s calculate the number of moles per liter at the pressure of 100 bar and 20 ° C:


p = 100 bar = 10,000 kPa (kilopascals)

V = 1 liter

R = 8.314472

T = 20 °C = 293.15 K

n = PV / RT = 4.10275


Looking at the formula we can see that double pressure means double number of moles:

200 bar pressure at 20 ° C = 8.2055 moles


The Ideal Gas assumptions define a direct proportionality between pressure and the amount of gas: with the same temperature, doubling the pressure and doubling the moles.


According to this assumption you would add the gases as "blocks" of pressure proportionally to the desired percentages, regardless of the kind of gas, the compositions of the initial mix and the target one and the sequence of gas.


Too good to be true ?  In fact it's not !

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