Compare and contrast the phase diagrams of water and carbon dioxide. Why doesn’t CO2 have a normal melting point and a normal boiling point, whereas water does? The slopes of the solid/liquid lines in the phase diagrams of H2O and CO2 are different. What do the slopes of the solid/liquid lines indicate in terms of the relative densities of the solid and liquid states for each substance? How do the melting points of H2O and CO2 depend on pressure? How do the boiling points of H2O and CO2 depend on pressure? Rationalize why the critical temperature for H2O is greater than that for CO2.