Question

A mixture of dry ice (i.e., solid CO2) and acetone (liquid) is commonly used in laboratories for cooling applications. You mix dry ice (1.00 kg at -78.2˚C) and acetone (1.00 kg at 25.0˚C) in a thermally well insulated container. The container is open such that CO2 may leave the flask. NOTE: CO2 at standard pressure sublimes (i.e. turns directly to the CO2 gas) at negative 78.2˚C. a. What is the final state of the mixture (phase and temperature of each substance)? b. What changes are to be expected if the amount of dry ice added to the system is doubled?

Answer 1

a. When added to acetone, dry ice will cool the acetone to the temperature of the dry ice. Inside flask at first glance it will be solid until changes of temperature make it liquid, so two phases are going to remain in equilibrium. Outside the flask it will be in gas phase. Since the mixture is used as a refrigerant the temperature of acetone will reached the solid C02 temperature and will be equal at equilibrium.

b. If you use the ideal gas law to find volume of this mixture you will find that volume of acetone will have an empirical volume of 2:1 where acetone will consume all solid CO2. If you double up the volume of dry ice, we can guees here, that the empirical volume will be 2:2 = 1:1. So we can say that the reaction for the mixture will be more slow and probably will take more time to dissolve CO2 in the acetone to reach the interested temperature.