1) No, it dose not liquefy and condenses to solid directly. At
1 atm pressure and at
−60∘C, CO2 lies ot the left of
−56.6∘C (triple point C). Hence, it lies in the region of vaporous and solid phases. Thus,
CO2 condenses into the solid state directly, without going though the liquid state.
2) At
4 atm pressure,
CO2 lies below
5.11 atm (triple point C.) Hence, it lies in the region of vaporous and solid phases. Thus , it condenses into the solid state directly , without passing through the liquid state.
3) When the temperature of a mass of solid
CO2 (at 10 atm pressure and at −65∘C) is increased , it changes to the liquid phase and then to the vaporous phase. It forms a line parallel to the temperature axis at
10 atm. The fusion and boiling points are given by the intersection points, where this parallel line cuts the fusion and vaporisation curves.
4) If
CO2 is heated to
70∘C and compressed isothermally, then it will not exhibit any transition to the liquid state. This is because
70∘C is higher than the critical temperature of
CO2. It will remain in the vapour state, but will depart from its ideal behaviour as pressure increases.