The Gas Law For Substances At High Temperature And Pressure Is Accomplished Via Van Der Waals Model

1373 Words Jul 28th, 2016 6 Pages
Improvements to the Ideal Gas law for substances at high temperature and pressure is accomplished via van der Waals model; which tweaks the ideal gas law formula by accounting for the volume the substances molecules and the intermolecular forces between molecules. These small changes greatly improve predicting the properties of pure substances, such as the solid/liquid/gas phase boundary for pure substances I was initially unclear as to the texts description explaining liquid-gas interaction, ... eventually a point is reached where there is no longer any discontinuous change from liquid to gas. This point is called the critical point, but upon further reflection its clear that above the critical point, temperature is not constant during phase change. In comparing the two states of carbon, diamond and graphite, the Gibbs free energy values for each are used to determine the most stable state. Diamond having a larger Gibbs free energy value is less stable than graphite and as such will spontaneously convert to graphite. Spontaneous is Entropy, but Gibbs free energy has pressure dependences, whats the connection? The change in Gibbs free energy is determined by holding temperature constant, but Entropy is a function of temperature solely. How is it that increasing pressure can change Gibbs free energy such that diamonds become more stable than graphite and as such change the spontaneous direction without a change in Entropy? Other key Ideas: Clausius-Clapeyron relation:…

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