Calorimetry: Heat of Fusion of Ice

HEAT OF FUSION OF ICE

When a chemical or physical change takes place, heat is either given off or absorbed. The change is either exothermic or endothermic. It is important for chemists to be able to measure this heat. Measurements of this sort are made in a device called a calorimeter. The technique used in making these measurements is called calorimetry.

In simplest terms, a calorimeter is an insulated container made up of two chambers. The outer chamber contains a known mass of water. In the inner chamber, the experimenter places the materials that are to lose or gain heat while undergoing a physical or chemical change. The basic principle on which the calorimeter works is that when two bodies at different temperatures are in contact with one another, heat will flow from the warmer body to the colder body. Thus, heat lost by one body will be gained by the other. This exchange of heat will continue until the two bodies are at the same temperature.

Unlike most calorimeters, the simple Styrofoam cup calorimeter used in this experiment will only have one chamber. The ice will be placed directly into a measured amount of water. The heat required to melt the ice will be supplied by the water. By measuring the temperature change (∆T) of the water, you can calculate the quantity of heat exchanged between the water and the ice. Using these experimental data, you will calculate the heat of fusion of ice.

Melting and freezing behavior are among the characteristic properties that give a pure substance its unique identity. As energy is added, pure solid water (ice) at 0C changes to liquid water at 0C.

In this experiment, you will determine the energy (in joules) required to melt one gram of ice. You will then determine the molar heat of fusion for ice (in J/g). Excess ice will be added to room temperature water, at a known temperature, in a Styrofoam cup. The room temperature water will be cooled down to a temperature near 0C by the ice. The energy required to melt the ice is removed from the room temperature water as it cools.

To calculate the heat that flows from the water, you can use the relationship:

Q = m ∆T Cp

Where Q stands for heat flow, Cp is the specfici heat capacity, m is the mass in grams, and the ∆T is the change in temperature. For water, the specific heat capacity of water is 4.18 J/g°C.

MATERIALS: 400 mL beaker250mL beaker100 mL graduated cylinder thermometer doubled Styrofoam cup scoopula

ice cubesstirring rod

SAFETY:Handle the thermometer with care. Handle warm glassware with care – check for heat using the back of your hand. The initial volume of water is very warm, do not burn yourself.

PROCEDURE:

1. Place the doubled Styrofoam cup into your 400 mL beaker to steady it.
2. Use your 100 mL graduated cylinder to obtain 100.0 mL of water at about 40°C from the back desk. Pour it into your Styrofoam cup assembly. Record this volume as V1.
3. Using another beaker, obtain 6-7 ice cubes from the igloo.
4. Place thermometer into the warm water but not touching the bottom. Hold it in the water for 30 seconds before taking the first temperature reading. Be sure to read to the thermometer to the tenths place.
5. At your start time, measure accurately and record the temperature of the water, T1. Immediately, add 2-3 ice cubes. Stir the ice-water mixture carefully with the thermometer. The cup should contain ice at all times. Therefore, if the last of the ice appears about to melt, add another ice cube.
6. Record the temperature of the ice-water mixture EVERY 30 SECONDS as you stir. Continue stirring (and adding ice, if necessary) until the temperature stops dropping and levels off to at least three readings.
7. Once it levels off, you are finished. Record this final temperature as T2.
8. IMMEDIATELY, carefully remove the unmelted ice with the scoopula. Allow any water removed with the ice to drain back into the cup.
9. Measure and record the volume of water in the cup, V2.

HEAT OF FUSION OF ICE

When a chemical or physical change takes place, heat is either given off or absorbed. The change is either exothermic or endothermic. It is important for chemists to be able to measure this heat. Measurements of this sort are made in a device called a calorimeter. The technique used in making these measurements is called calorimetry.

In simplest terms, a calorimeter is an insulated container made up of two chambers. The outer chamber contains a known mass of water. In the inner chamber, the experimenter places the materials that are to lose or gain heat while undergoing a physical or chemical change. The basic principle on which the calorimeter works is that when two bodies at different temperatures are in contact with one another, heat will flow from the warmer body to the colder body. Thus, heat lost by one body will be gained by the other. This exchange of heat will continue until the two bodies are at the same temperature.

Unlike most calorimeters, the simple Styrofoam cup calorimeter used in this experiment will only have one chamber. The ice will be placed directly into a measured amount of water. The heat required to melt the ice will be supplied by the water. By measuring the temperature change (∆T) of the water, you can calculate the quantity of heat exchanged between the water and the ice. Using these experimental data, you will calculate the heat of fusion of ice.

Melting and freezing behavior are among the characteristic properties that give a pure substance its unique identity. As energy is added, pure solid water (ice) at 0C changes to liquid water at 0C.

In this experiment, you will determine the energy (in joules) required to melt one gram of ice. You will then determine the molar heat of fusion for ice (in J/g). Excess ice will be added to room temperature water, at a known temperature, in a Styrofoam cup. The room temperature water will be cooled down to a temperature near 0C by the ice. The energy required to melt the ice is removed from the room temperature water as it cools.

To calculate the heat that flows from the water, you can use the relationship:

Q = m ∆T Cp

Where Q stands for heat flow, Cp is the specfici heat capacity, m is the mass in grams, and the ∆T is the change in temperature. For water, the specific heat capacity of water is 4.18 J/g°C.

MATERIALS: 400 mL beaker250mL beaker100 mL graduated cylinder thermometer doubled Styrofoam cup scoopula

ice cubesstirring rod

SAFETY:Handle the thermometer with care. Handle warm glassware with care – check for heat using the back of your hand. The initial volume of water is very warm, do not burn yourself.

PROCEDURE:

1. Place the doubled Styrofoam cup into your 400 mL beaker to steady it.
2. Use your 100 mL graduated cylinder to obtain 100.0 mL of water at about 40°C from the back desk. Pour it into your Styrofoam cup assembly. Record this volume as V1.
3. Using another beaker, obtain 6-7 ice cubes from the igloo.
4. Place thermometer into the warm water but not touching the bottom. Hold it in the water for 30 seconds before taking the first temperature reading. Be sure to read to the thermometer to the tenths place.
5. At your start time, measure accurately and record the temperature of the water, T1. Immediately, add 2-3 ice cubes. Stir the ice-water mixture carefully with the thermometer. The cup should contain ice at all times. Therefore, if the last of the ice appears about to melt, add another ice cube.
6. Record the temperature of the ice-water mixture EVERY 30 SECONDS as you stir. Continue stirring (and adding ice, if necessary) until the temperature stops dropping and levels off to at least three readings.
7. Once it levels off, you are finished. Record this final temperature as T2.
8. IMMEDIATELY, carefully remove the unmelted ice with the scoopula. Allow any water removed with the ice to drain back into the cup.
9. Measure and record the volume of water in the cup, V2.