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.

Question

Krista Fox

Chemistry

20 February, 12:08

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.

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Corinne Li · Answer 1

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