4. a calorimeter contains 500 g of water at 25°c. you place a hand warmer containing 200 g of liquid sodium acetate inside the calorimeter. when the sodium acetate finishes crystallizing, the temperature of the water inside the calorimeter is 39.4°c. the specific heat of water is 4.18 j/g-°c. what is the enthalpy of fusion (hf) of the sodium acetate? (show your work.) where necessary, use q = mhf.

First, we must calculate the energy released by the sodium acetate by assuming all the heat released is absorbed by the water. The heat absorbed by the water is given by:
Q = mcΔT
Q = 500 * 4.18 * (39.4 - 25)
Q = 30,096 J = 30.096 kJ

The enthalpy of fusion is expressed in kJ/mol, so we must first calculate the moles of sodium acetate using:
moles = mass / Mr
moles = 200 / 82.03
moles = 2.44 mol

ΔHf = -30.096 / 2.44
ΔHf = -12.33 kJ/mol