[benjster85]

Why does the temperature remain at -78˚C? I know that that is the temperature at which CO2 sublimes; so I understand why it stops subliming once the acetone reaches that temperature. However, I don't understand why the acetone does not get colder; presumably the bulk of the dry ice is COLDER than -78˚C, right?

[Yggdrasil]

How would the dry ice sublime if it is colder than its sublimation point?

[benjster85]

As a senior member of this forum, I know you know your stuff. I don't, and that is why I'm asking.

My question is: the CO2 is very cold; it is cooling off the acetone, even as the acetone is heating it. Once -78˚C is reached, why doesn't the acetone's temperature continue to drop. It is in contact with the very cold CO2, after all....

[AWK]

I think that limiting factor in cooling bath with dry ice or liquid nitrogen may be the melting point of  solvent or boiling point of mixture CO2(N2)-solvent.

[Enthalpy]

Why should the dry ice be colder than -78°C?
If produced colder, it reaches -78°C during storage because at that temperature, it can absorb enough heat by sublimation to stay cold.

[AWK]

Why should the dry ice be colder than -78°C?
If produced colder, it reaches -78°C during storage because at that temperature, it can absorb enough heat by sublimation to stay cold.

Dry ice itself sublimes (- 78.5 C), cooling bath - dry ice or liquid nitrogen with chloroform (-61 C or -63 C, respectively; melting point of chloroform -63.5 C).
Dry ice in acetone (-78 C) or ethyl ether (-100 C) dissolves first, then its solution boils.