Which of the following are true statements ?

Question

a) The triple point of CO2 is -57oC and 5 atm
b) CO2 boils at 73 atm and about -50oC
c) The melting temperature of a substance is more dependent on pressure than is its boiling boint
d) At 5 mm Hg and 100oC H2o=O is only in the gas phase

Answer 1

The triple point of CO2 is approximately 518 kPa at −56.6°C, which is very close to 5 atm and -57°C, so it's safe to say that a) is true. Looking at a phase diagram for CO2, it looks like b) is unture; CO2 should still be a liquid under those conditions. c) is untrue; in fact, the boiling temperature has a greater dependence on pressure than does the melting temperature. d) is true, though; water boils at 100°C at 760 mm-Hg, and lower pressures only lower the boiling temperature. So at a pressure as low as 5 mm-Hg, water would exist only as vapor.