38 - A P CHEMISTRY Lab 6-1 Determination of a Calorimeter...

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A P CHEMISTRY Lab 6-1 Determination of a Calorimeter Constant Pre-Lab Questions - (Must be completed before lab work begins.) 1. What is the definition of the joule in terms of the basic SI units? 2. A calorimeter is to be calibrated: 51.203 g of water at 55.2 o C is added to a calorimeter containing 49.783 g of water at 23.5 o C. After stirring and waiting for the system to equilibrate, the final temperature reached is 37.6 o C. Calculate the calorimeter constant. INTRODUCTION Chemical and physical changes are always accompanied by a change in energy. Most commonly, this energy change is observed as a flow of heat energy either into or out of the system under study. Heat flows are measured in an instrument called a calorimeter. There are specific types of calorimeters for specific reactions, but all calorimeters contain the same basic components. They are insulated to prevent loss or gain of heat energy between the calorimeter and its surroundings. For example, the simple calorimeter you will use in this experiment is made of a heat-insulating plastic foam material. Calorimeters contain a heat sink that can absorb or provide the energy for the process under study. The most common material used as a heat sink for calorimeters is water, because of its simple availability and large heat capacity. Calorimeters also must contain some device for the measurement of temperature, because it is from the temperature change of the calorimeter and its contents that the magnitude of the heat flow is calculated. Your simple calorimeter will use an ordinary thermometer for this purpose. To determine the heat flow of a process, the calorimeter typically is filled with a weighed amount of water. The process that releases or absorbs heat is then performed within the calorimeter and the temperature of the water in the calorimeter is monitored. From the mass of water in the calorimeter, and from the temperature change of the water, the quantity of heat transferred by the process can be determined. The calorimeter for this experiment will be demonstrated. The calorimeter consists of two nested plastic foam coffee cups and a cover, with thermometer and stirring wire inserted through holes punched in the cover. As you know, plastic foam does not conduct heat well and will not allow heat generated by a chemical reaction in the cup to be lost to the room. (Coffee will not cool off as quickly in such a cup as in a china or paper cup.) The simple coffee-cup calorimeter generally gives quite
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This note was uploaded on 08/31/2010 for the course SCI 56-1120 taught by Professor Unni during the Spring '09 term at Columbia College.

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38 - A P CHEMISTRY Lab 6-1 Determination of a Calorimeter...

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