Heat of Fusion Lab Chemistry p.2
Molar Heat of Fusion of Ice
We are melting an ice cube, you really need Directions!
The amount of energy required to convert a solid to a liquid, at constant temperature and pressure is known as the heat of fusion. It is often useful to refer to the amount of heat needed per gram or per mole of substance. The molar heat of fusion is therefore the energy needed to change one mole of a solid into liquid at the melting point and is specific to that substance.
H2O (s) + molar heat of fusion à H2O (l)
You will perform an experiment to determine the molar heat of fusion of ice. Ice will be placed in a calorimeter (styrofoam cup) with a known amount of WARM water. The volume (this is made easy by the fact that 1 ml of water weights one gram) of the melted ice and water in the cup will be used with temperature data for the calorimeter to calculate the molar heat of fusion of ice.
Objectives: To determine the molar heat of fusion of ice.
Pre-lab: Complete on a separate sheet, and prepare a data table for this lab.
Materials:
2 styrofoam cups 600 mL beaker water
100 mL graduated cylinder 150 mL beaker thermometer 1 ice cube
Procedure:
1. Place a dry styrofoam cup into a beaker for support. Have all your equipment ready including your CRUSHED ice cubes in a separate styrofoam cup. Now weigh the NESTED cups
2. Obtain about 100 mL of water, weigh it
3. Record temp of water, and THEN add ice cube, one cube , not too much.
4. Record the exact temperature of the water and immediately add ice cubes to the cup. Make sure you add only ice, not water. Also be careful not to splash!
5. Stir constantly and monitor the temperature in the middle of the water near the floating ice (not on the bottom). Watch the temperature go down and observe that the ice is melting. You are waiting until the temperature of the ice and water pretty much stops going down.
6. Clean-up / disposal... leave your equipment to dry on the rack.
PUT ALL DATA COLLECTED IN A DATA TABLE, Remember to use sig figs!
1. Calculate the heat of fusion in the following units: cal/g cal/mol kJ/mol KJ/g
2. What was your percent error? (Be sure to get or look up the accepted value to 2 SF)
3. If you repeated the experiment with 10 mL less hot water, how would the molar heat of fusion be expected to differ (higher, lower, or the same?) Explain.
4. If heat was lost from your calorimeter (styrofoam cup) while the ice was melting, would it have made the value for the molar heat of fusion that you calculated higher or lower than the accepted value? Explain clearly.