Suppose a bag full of ice (450 g) at 0.0 °C sits on the counter and begins to melt to liquid water. How much energy must be absorbed by the ice if 2/3 of it melted?
All you have to do here is figure out how much heat is required to convert ice at
#DeltaH_f = 334"J"/"g"#
What that means is that in order to melt
In your case, you need to know how much heat is required to melt
#2/3 * 450 color(red)(cancel(color(black)("g"))) * "334 J"/(1color(red)(cancel(color(black)("g")))) = "100,200 J"#
Rounded to two sig figs and expressed in kilojoules, the answer will be
#q = color(green)(1.0 * 10^2"kJ")#