The Heat of Fusion of Water
Laboratory #5
Discussion
It is has been long established that exactly 334 Joules of heat energy are needed to change 1 gram
of ice, H2O (s), at 0.0oC to liquid water, H2O (l) at 0.0oC. How can we calculate this?
We remember that the amount of energy lost by one object, -q, is equal to the gained by another
object, q, if heat flow occurs only between those objects. In this laboratory, energy will be
flowing from water at room temperature to ice at 0.0oC. This is summarized by
- qlost by water = qgained by ice
We can figure out water’s energy loss using q = m x c x dt
Water’s loss is ice’s gain.
q = m x Hf
In short, if we know how much energy water has lost, and energy ice has gained, and the mass of
the ice, we can experimentally find Hf for ice
Materials
Styrofoam cups (2), nested
100 mL of water
Cup of ice
thermometer
graduated cylinder
Procedure
(1)
(2)
(3)
(4)
(5)
Measure out 100.0 mL of water, and pour into a Styrofoam cup.
Place thermometer into cup. Take initial temperature, and record as Ti.
Add two ice cubes to cup. As soon as the ice melts, put more ice into
the cup. In short, make sure your cup has solid ice at all times.
Once the temperature stops falling, remove any unmelted ice.
Measure the total volume of water in the cup using your graduated cylinder.
Data
1.
2.
3.
4.
Re-copy this Data Table on your Report Sheet
Initial volume of water, Vi
Final volume of water, Vf
Initial temperature of water, Ti
Final temperature of water, Tf
Calculations
1.
2.
3.
4.
5.
6.
_____
_____
_____
_____
Re-copy your Calculations on your Report Sheet. SHOW ALL WORK.
Volume of Ice melted =
Vf - Vi
Mass of Ice melted
=
Volume of Ice Melted
Mass of Water
=
Vi
TH2O
=
Tf - Ti
Energy lost by water (qH2O) = massH2O x cH2O x TH2O
Energy gained by ice (qice) = Energy lost by water (qH2O)
=
=
=
=
=
=
____________
____________
____________
____________
____________
____________
7.
Hf of water = qice / massice
=
____________
8.
The accepted heat of fusion for ice is 334 J/g. Calculate your % error.
Conclusion Questions Write Answers on your Report Sheet in Complete Sentences.
1.
How were we able to determine the amount of energy gained by ice during the phase
change?
2.
Make a sketch of the ice and water in the cup, and show the direction of heat flow in
the system.
3.
A 200.0 gram sample of water decreases from 90.0oC to 50.0oC.
(a) Calculate the amount of energy in Joules released by the cooling water using q =
mcT.
(b) A piece of H2O (s) at 0oC absorbs the energy from the cooling water in (a),
and changes to H2O (l) at 0oC. Using q = m Hf, calculate the mass of ice that
melted.
4.
Purpose
Did all of the heat flow occur only in the cup? If not, explain how this might affect
our calculation of the energy lost by the water, and absorbed by the ice.
Write a one-sentence purpose on your Report Sheet
Conclusion Paragraph
Write on your Report Sheet in Complete Sentences
In a splendid 4 sentence conclusion paragraph, state your results, and whether your results
confirm that the Hf of ice is 334 J/g K. Describe any sources of error beyond your control (not
Leblanc doesn’t know how to read a thermometer or Sagar messed up) that might have caused the
% error you calculated.
Grading of Lab Report Sheet
Lab #, Lab Title, Name, Date
Purpose
Conduct
Data
Calculations
Conclusion Questions
Conclusion Paragraph
5%
10%
10%
20%
25%
20%
10%