# What is the heat flow involved for #"250 mL"# of water that freezes? #DeltaH_f = "6.02 kJ/mol"#. Assume the density of water is #"1.00 g/mL"# at this temperature.

##### 1 Answer

Well, you have restricted yourself to two sig figs, so I get

(What is the system?)

Freezing is a **phase equilibrium** where the temperature and pressure are constant. With ** constant pressure**, we have

#q = DeltaH# , provided the units are the same.

Thus, we have the relationship

#barul(|stackrel(" ")(" "q = n_wDeltaH_f" ")|)# where

#q# is the heat flowout of#n_w# mols of ice that corresponds to a molar enthalpy of fusion#DeltaH_f# at#0^@ "C"# .

The density of water at

Therefore, the **heat flow involved** is

#color(blue)(q) = overbrace((250 cancel"mL" xx cancel"1.00 g"/cancel"mL" xx (cancel"1 mol")/(18.015 cancel"g")))^(n_w) xx overbrace((-"6.02 kJ"/cancel"mol"))^(DeltaH_f)#

#=# #color(blue)(-83._(54) " kJ"#

to two sig figs, you'd get *released*.