[Flux]

Question: The triple point of carbon dioxide is -57 degree Celsius and 5.1 atmospheric pressure. This implies that

1 the normal melting point of dry ice (solid carbon dioxide) is 0 degree Celsius

2 dry ice sublimes at room temperature

3 dry ice melts when it is slowly heated at 10atm

Choose the possible answers.

Although my book have the exact same diagram for the phase diagram of carbon dioxide, but the question tells me that I have to reason it out because of the word "implication". However, I really can't figure much about the relationships of the phase changes with the triple point.

Your effort in teaching me to relate triple point and deciphering it to get more information is greatly appreciated!

Answer: is 2 and 3

EDIT: Extra question

Why does liquid changes rapidly into vapour and bubles of vapour are formed inside the liquid when the vapour pressure is same as the atmospheric pressure.

What is the implication? I know this happens during boiling, but how does a same vapour pressure and external pressure make the liquid change to vapour faster?

[MrTeo]

EDIT: Extra question

Why does liquid changes rapidly into vapour and bubles of vapour are formed inside the liquid when the vapour pressure is same as the atmospheric pressure.

What is the implication? I know this happens during boiling, but how does a same vapour pressure and external pressure make the liquid change to vapour faster?

The speed at which it becomes vapor depends only on the amount of heat given to the compund... when you boil some water, if the temperature is constant a higher flame means a higher evaporation rate...
The fact that the external pressure is equal to the vapor pressure only causes the formation of bubbles INSIDE the liquid, while when the temperature is lower than t_eb, evaporation happens only at the surface...

[vmelkon]

I don't think you need to reason it out. You just need to look at the phase diagram.
3. Increasing the pressure would mean the temperature range CO2 exists as a liquid expands. Also, increasing the pressure to 10 atm at -57 C would be CO2 can exist as a solid only. Heating it a few degrees higher would melt it.
Also notice that the slope between solid/liquid is positive.

"Why does liquid changes rapidly into vapor and bubbles of vapor are formed inside the liquid when the vapor pressure is same as the atmospheric pressure."

Normally, we heat the flask or whatever from the bottom so it bubble from the bottom. Nothing special.