UTD CHEM 1111 - Laboratory 12 CALORIMETRY (17 pages)

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Laboratory 12 CALORIMETRY



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Laboratory 12 CALORIMETRY

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Pages:
17
School:
The University of Texas at Dallas
Course:
Chem 1111 - General Chemistry Laboratory I
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Laboratory 12 CALORIMETRY Objectives 1 Construct and utilize a coffee cup calorimeter to measure heat changes 2 Determine the heat capacity of a calorimeter 3 Determine the specific heat of an unknown metal sample Energy Transformations Thermochemistry concerned with heat changes that occur during chemical reactions Energy capacity for doing work or supplying heat weightless odorless tasteless if within the chemical substancescalled chemical potential energy Energy Transformations Heat represented by q is energy that transfers from one object to another because of a temperature difference between them only changes can be detected flows from warmer cooler object Exothermic and Endothermic Processes Essentially all chemical reactions and changes in physical state involve either a release of heat or b absorption of heat Exothermic and Endothermic Processes In studying heat changes think of defining these two parts the system the part of the universe on which you focus your attention the surroundings includes everything else in the universe Heat flowing into a system from it s surroundings defined as positive q has a positive value called endothermic system gains heat gets warmer as the surroundings cool down Heat flowing out of a system into it s surroundings defined as negative q has a negative value called exothermic system loses heat gets cooler as the surroundings heat up Units for Measuring Heat Flow 1 A calorie is defined as the quantity of heat needed to raise the temperature of 1 g of pure water by 1 oC 2 The calorie is also related to the Joule the SI unit of heat and energy named after James Prescott Joule 4 184 J 1 cal Heat Capacity the amount of heat needed to increase the temperature of an object exactly by 1 oC Depends on both the object s mass and its chemical composition Specific Heat Capacity abbreviated C The amount of heat it takes to raise the temperature of 1 gram of the substance by 1 oC often called simply Specific Heat Note the tremendous difference in Specific Heat Thus for water it takes a long time to heat up and it takes a long time to cool off Water s value is VERY HIGH Heat Capacity and Specific Heat To calculate use the formula q mass in grams x T x C heat is abbreviated as q T change in temperature C Specific Heat Units are either J g oC or cal g oC Calorimetry Calorimetry the measurement of the heat into or out of a system for chemical and physical processes heat released heat absorbed The device used to measure the absorption or release of heat in chemical or physical processes is called a Calorimeter A foam cup calorimeter here two cups are nestled together for better insulation Calorimetry Changes in enthalpy H q H Thus q H m x C x T H is negative for an exothermic reaction H is positive for an endothermic reaction Assigned Reflection Questions Questions 1 2 3 and 4


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