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Summary Heat of Fusion and Melting Ice Experiment
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Heat of Fusion and Melting Ice Experiment
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Experiment 4-Heat of Fusion and Melting Ice ExperimentIn this lab, the heat of fusion for water will be determined by monitoring the
temperature changes while a known mass of ice melts in a cup of water. The
experimentally determined value for heat of fusion will be compared with the accepted
standard value. We will also explore the following question regarding the rates of melting
for ice cubes is posed: Will ice cubes melt faster in distilled water or in salt water?
Part A-Heat of Fusion
A phase change is a term physicists use for the conversion of matter from one of its
forms (solid, liquid, gas) to another. Examples would be the melting of solid wax to a
liquid, the evaporation of liquid water to water vapor, or condensation of a gas to a liquid.
The melting of a solid to a liquid is called fusion.
As a phase change occurs, say the evaporation of boiling water, the temperature of
the material remains constant. Thus, a pot of boiling water on your stove remains at 100
°C until all of the water is gone. Even if the pot is over a big flame that is 900 °C, the
water in the pot will only be 100 °C. A tray of water in your freezer will approach 0 °C
and remain at that temperature until the water is frozen, no matter how cold the freezer is.
In a phase change, heat energy is being absorbed or emitted without changing the
temperature of the material.
The amount of energy that is absorbed or emitted during a phase change obviously
depends on the mass of the material undergoing the change. It takes more energy to melt
a bag of ice than it takes to melt a single ice cube. The amount of energy also depends on
the substance, because of the particular composition of each substance. It takes 80
calories of heat energy to melt 1 g of ice. This is the heat of fusion (Hfusion) for ice (heat
required per gram of substance).
In order to determine the heat of fusion for ice, we need to melt some ice and
measure how much heat energy is absorbed. The ice needs to be isolated from its
surroundings, so we place it in an insulating Styrofoam cup, which is a simple device
called a calorimeter (heat measurer). Measuring changes in heat energy is simply
measuring changes in temperatures. Warm water will be used in the Styrofoam cup to
melt the ice. Recall that the mass of the ice is important. It is hard to weigh ice without
melting some of it, so the mass of the ice will be determined after it has melted. As ice
melts (at a constant temperature of 0 °C), it forms water at 0 °C, absorbing heat energy
form the warm water. This cold water then needs to be warmed, which absorbs more
heat energy form the warm water, until a final temperature is reached. The heat lost by
the warm water must be equal to the heat gained by the ice and cold water.
The property of specific heat (Hsp) is the amount of heat energy needed to change
the temperature of one gram of a material by one degree Celsius. Like Hfusion, the value
of Hsp depends on the substance. For example, it takes much more energy to heat up a
pot full of water than it does to heat up the metal of the pot itself. Hsp for water is 1
calorie/ g °C.
, 20 Experiment 4-Heat of Fusion and Melting Ice Experiment
Hypothesis: What is the heat of fusion for water?
Experiment:
Materials: ice, 400 ml beaker, hot plate, thermometer, Styrofoam cup and lid, distilled
water
SAFETY:
Use caution when working near the hot plate to avoid burns. Ice is slippery.
Procedure:
Remember, you are trying to replicate numbers obtained by professional scientists! Be
careful to make accurate measurements!
1. Fill the 400 mL beaker about half full of distilled water and heat on the hot plate to
about 40-45 °C.
2. Insert the thermometer into a bucket of ice and allow the temperature to stabilize.
Record the temperature, which is Tice, in row 6
3. Assemble the Styrofoam cup calorimeter and put on the cover, and record the mass
in row 1.
4. Fill the inner cup about half full with warm, distilled water. Replace the cover and
record the mass of the calorimeter + warm water in row 2.
5. Insert the thermometer into the calorimeter, stir for 1 min, and record the
temperature, Tw, in row 7.
6. Get two ice cubes, pat dry with a paper towel, and carefully place into calorimeter. Be
careful not to touch the ice with your bare fingers, since this will melt the ice. Don’t let
it splash!!
7. Quickly cover the calorimeter and stir with the thermometer until all of the ice has
melted. The temperature should drop down to 8-12 °C. If it doesn' t, add more ice.
8. Observe the thermometer, and record the minimum temperature that it displays as Tfinal
in row 8.
9. Remove the thermometer and record the mass of the calorimeter, cover and cool water,
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