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Physics of Hydrogen under great Pressure

# Physics of Hydrogen under great Pressure - The difficult...

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Physics of Hydrogen under great Pressure For the van der Waals regime we modify this so that P=RT/V becomes: P = [RT/(v-b)] - a/v 2 This van der Waals equation of state has to be modified further once P>P c and T>T c (supercritical), to give: The Dieterici equation of state near the critical point is complex so one often uses the simpler Berthelot equation: P = [RT/(v-b)] - a/Tv 2 which improves over the van der Waals equation. Thisr the van der Waals equation. This Berthelot equation is often rewritten using reduced variables: More complex, less physical and more accurate are the virial equations of state: PV = RT(1 + b/V + c/V 2 + d/V 3 .... ) and the Beattie-Bridgman equation: PV = RT + B/V + C/V 2 + D/V 3 + ..... where B=B(T), C=C(T), D=D(T) etc.

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Unformatted text preview: The difficult part can be finding the values for the coefficients once we reach pressure regimes that are not reachable in the Lab, as then we have to rely on theory alone. If we combine all the information we have about the behaviour of hydrogen under pressure and then use theory to try to extrapolate to great pressures we can predict what will happen as a body grows by accumulating more and more Hydrogen: This calculation is very complex and difficult so for this diagram we have had to make some simplifying assumptions. Thus this is for a body at 0K, and it is a spherical, non-rotating body composed of pure hydrogen. Bodies at non-zero temperature would be larger and so the curve would move to the right....
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