Question

This was a lab over phase changes. We dropped 20 ml of ice, 40 ml of liquid nitrogen, and 15 ml of dry ice into a styrofoam cup containing about 60 ml of 55-65 degree celsius water (not all at the same time, but respectively). Can someone help me out with these lab questions?

Of the three processes you investigated today, which involved the greatest amount of heat per mole for the phase changes involved?

Are the phase changes investigated exothermic or endothermic?

Does the amount of heat involved depend upon the amount of material being melted, vaporized, or sublimed?

Do you think the amount of heat involved depends upon the identity of the substance being melted, vaporized, or sublimed?

What intermolecular changes are occurring?

Answer 1

1) Liquid nitrogen has the highest specific heat capacity than dry ice followed by ice .That means nitrogen will absorb more amount of heat for a given temperature change .Hence,the greatest amount of heat per mole for phase changes is involved in the process of adding liquid nitrogen.

2)Since the process is conducted in open atmosphere therefore the process is endothermic as cold substances will absorb heat from surrounding.

3) Yes , the amount of heat involved depends on amount of substances as we can conclude from the formula

heat= moles*(specific heat capacity per mole)* (change in temperature)

4) The coolent(ice, liquid nitrogen or dry ice) absorbs heat that results in more vibration of their molecules due to which the intermolecular attraction decreases and in case of water that gets cools down the force of attraction between molecules increases.