Sunday, June 5, 2011

Effect of Pressure


The extent of deviations which real gases show from Ideal behaviour at different pressures can be studied from the graph plotted for different gases between compressibility factor and pressure keeping temperature constant.
Two types of curves are generally obtained:
(1). For gases like hydrogen and helium, the compressibility factor is continuously increasing with increase in pressure. That is, they always show positive deviation.
(2). For gases like CO2, O2, N2, CH4 the compressibility factor first decreases with increase in pressure reaches a minimum value and then begins to increase. Therefore, for these gas, Z < 1(negative deviation) at low pressure and Z > 1(positive deviation) at high pressure.

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