How do I best calculate and plot the vapour pressure?
If the substance vaporizes to form a single gaseous species of the same composition then you can use the Reaction module. Simply enter the reaction, for example H2O(liq) = H2O(gas), and select isothermal calculations. The calculated equilibrium constant is equal to the vapour pressure. Use Equilib for real systems possibly involving dissociation (CaCO3) or polymerization (Na). In the Reactants Window enter your initial substance, e.g. CaCO3 or Na. Then in the Menu Window set the temperature range (e.g 500 1200 100), leave the pressure box undefined (blank), fix a constant volume ‘Product V’ (small enough that some condensed substance remains – say 1.0), and then click the calculate button. For the gas phase that is formed the total pressure is given. That is the pressure that can also be measured experimentally (for example in a torsion Knudsen effusion apparatus). Furthermore the partial pressures of the possible gas species are given thus simulating a mass spectrometric analysis of t
