When heat is transferred to an object, the temperature of the object increases. When heat is removed from an object, the temperature of the object decreases. The relationship between the heat ( q ) that is transferred and the change in temperature ( ΔT ) is
q = C ΔT = C ( Tf - Ti )
The proportionality constant in this equation is called the heat capacity ( C ). The heat capacity is the amount of heat required to raise the temperature of an object or substance one degree. The temperature change is the difference between the final temperature ( Tf ) and the initial temperature ( Ti ).
|heat||q||joule (J)||Energy transfer that produces or results from a difference in temperature|
|temperature||T||oC or K||Measure of the kinetic energy of molecular motion|
|temperature change||ΔT||oC or K||Difference between the final and initial temperatures for a process|
|heat capacity||C||J oC-1 or J K-1||Heat required to change the temperature of a substance one degree|
A calorimeter is an experimental device in which a chemical reaction or physical process takes place. The calorimeter is well-insulated so that, ideally, no heat enters or leaves the calorimeter from the surroundings. For this reason, any heat liberated by the reaction or process being studied must be picked up by the calorimeter and other substances in the calorimeter.
A thermometer is typically inserted in the calorimeter to measure the change in temperature that results from the reaction or physical process. A stirrer is employed to keep the contents of the calorimeter well-mixed and to ensure uniform heating.
The calorimeter shown below contains some water and is equipped with a thermometer, a stirrer, and a heating element. When activated, an electric current is passed through the heating element to generate heat, which is transferred to the calorimeter. In this
simulation, you can set the heating rate (units of J sec-1) and the heating time (units of sec).
|Calorimeters include two vessels. One is known as an outer vessel and the other is known as an inner vessel. The air between the inner vessel and the outer vessel works as a heat insulator, so there is no or very little heat exchange between the contents of the inner vessel with the outside.
It also contains a thermometer and a stirrer. The thermometer is used to measure the temperature of the liquid (usually water) in the inner vessel. The stirrer is used to stir the liquid and distribute heat in the vessel.
Calorimeters have a fiber ring that hold the inner vessel hanging in the center of the outer vessel. The fiber ring is made of insulating fiber material.
Finally, each calorimeter has an insulating cover or lid with holes for the stirring rod and thermometer.
|How to assemble your calorimeter?
Start by assembling the vessels. Place the fiber ring in the larger vessel and then insert the small vessel in the center of the fiber ring.
Insert the thermometer in the center hole of the lid or insulating cover; position it so that when you close the cover, the bulb of the thermometer will be in the center of the lower vessel, about one inch from the bottom.
Insert the stirring rod and attach the handle of the insulating rod.
How to use your calorimeter to measure the specific heat of Iron?
Fill the inner vessel with 125 ml water. Close the lid and leave it for about 30 minutes. At this time the bulb of the thermometer must be in the water. (If it is not, push the thermometer lower). After 30 minutes, read and record the water temperature.
Fill up a test tube half way with iron nails. Weigh and record the weight of the nails. Place the test tube with nails in hot-boiling water for about 10 minutes. This will allow the nails to get to 100ºC temperature without getting wet.
Open the lid of the calorimeter and transfer the nails to the inner vessel. Immediately close the lid. Move the stirrer up and down and read the temperature. Record the highest temperature. This will be the final temperature of the water and nails.
Calculate the temperature increase of water and temperature loss of iron nails.
Multiply the temperature increase of water by 125 ml of water to calculate the total heat transfer in calories.
Divide the total heat transfer by the temperature loss of iron; then divide the results by the weight of iron to calculate the specific heat of iron.
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