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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.

Respuesta :

scme1702
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

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