Heat of Fusion
Background Information
The heat of fusion is the energy required to melt 1 mol of a
substance. Ice and water can coexist at the freezing point. To melt
the ice, energy must be added. The heat absorbed by a melting a
solid increases the potential energy of the solid as its particles are
pulled apart in opposition to the attractive forces tending to hold
them together. As you go from a solid to a liquid to a gas, a
decrease in the order of the atoms will occur. Gases do not need to
be held in place. In this lab, you will determine the amount of heat
required to melt one gram of ice.
KNOW: What do you know about the heat of fusion?
Objectives
-Identify correct lab procedures to evaluate phase change.
-Calculate heat of fusion of water.
-Compare known values to experimental values.
Procedure
1. Place 75 g of water at room temperature in your calorimeter, and
record the temperature of the water. Remember that 1 mL = 1 g.
2. Remove the water from several ice chips from the freezer and
add them to the room temperature water(use a paper towel for
this).
3. Gently stir the ice as it melts—slowly add more ice if necessary
as there should always be some present until the temperature
reaches 0 ºC.
4. When the temperature of the ice-water mixture is 0 ºC, use a
plastic spoon to remove any excess ice in the calorimeter. Don’t
take any water with it.
Make sure to drain all of the water from your ice before removing
the ice from the calorimeter.
5. Measure and record the final mass of the water.
Data
Initial temperature:
Final temperature:
Initial mass: 75 g
Final mass:
Calculations
1. Determine the heat transferred from the water to the ice:
Mass water × specific heat of water × change in temperature
2. According to your results, how much heat is required to melt a
gram of ice?
(This is your heat of fusion)
Heat transferred/mass of ice
3. The actual value for the heat of fusion of ice is 330 J/g.
Determine the percent error in your value.
(Actual-experimental)/actual × 100
Answer two analysis questions with complete sentences.
1. Why would you not want to stir the ice vigorously in the
calorimeter?
2. Why would you want to wipe the ice off before placing it in the
calorimeter?
3. What are some possible sources of human error in the
experiment?
LEARN: What did you learn about the heat of fusion?