A 154 g sample of water at 0oC freezes into ice at °C How many joules (J) of energy are needed for the phase change?
Since you don't give the temperature of the ice, I'll assume it to be
Note: technically the energy is NOT needed. This is the energy released by the liquid water at
The only information you need to solve this problem is the value of water's enthalpy of fusion,
This value tells you that, for every gram of water, 333.5 J will be given off to transform it from liquid to solid, i.e. make it undergo a phase change.
Since you've got 154 g, the total energy needed will be
Rounded to three sig figs, the number of sig figs given for 154 g, and keeping in mind that the energy is given off, you can say that