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Experiment #4 - Calorimetry .doc

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Department
Chemistry
Course
CHEM 120L
Professor
Sue Stathopulos
Semester
Fall

Description
Coffee Cup Calorimetry: Enthalpy of Neutralization Due: Thursday November 22, 2012 Due: November 14th, 2012 Introduction The purpose of this experiment is to determine the molar enthalpy of neutralization, and calculate the unknown concentration of the HCl. Changes in energy are always associated with chemical reactions. (Clancy et at., 2011). If energy is liberated in the form of heat the reaction is said to be exothermic. (Reece, 2011). If energy is absorbed, it is endothermic. (Reece, 2011). Thermochemistry is the branch of chemistry which deals with the gain or loss of heat. (Clancy et at., 2011). Acalorimeter is used to measure these changes in heat. (Clancy et at., 2011). It is an insulated container, in which a reaction can occur and the temperature can be measured. (Clancy et at., 2011).A simple coffee cup calorimeter is used in this experiment. The coffee cup is not a sealed system, and therefore the internal pressure is the same as the atmospheric pressure. (Clancy et at., 2011). It can be said that the pressure of the reactants initially, q (heat of reaction) is equal to the final pressure of the system △H (enthalpy change). (Clancy et at., 2011). All strong electrolytes completely dissociate in solutions.As long as the acid and base completely dissociate, the heat of neutralization will not be effected. Neutralization reactions are usually exothermic and have a negative △H for strong electrolytes. They can be modeled using the formula: H⁺ + OH⁻ --> HOH where q= -55.90 kJ per mol of H⁺. (Clancy et at., 2011).At a constant pressure, the heat of reaction is equal to the enthalpy change. Therefore △H is -55.90 kJ per mol of H⁺. (Clancy et at., 2011). For a weak electrolyte, the reaction is endothermic with a q of 25.3kJ/mol. Experimental Procedure The experiment was outline in the CHEM 120L lab manual, Experiment #4. All steps were followed without deviations. Results Table #1 Average Temperature of the Acid and Base Experiment TemperatureofAcid TemperatureofBase AverageTemperature (°C) (°C) ofAcidandBase(°C) Part A Trial #1 21.8 21.5 21.7 Experiment TemperatureofAcid TemperatureofBase AverageTemperature (°C) (°C) ofAcidandBase(°C) Part A Trial #2 22.1 21.9 22.0 Part B Trial #1 22.2 22 22.1 Part B Trial #2 22.1 21.8 22.0 Part C Trial #1 22.1 22.4 21.8 Part C Trial #2 21.9 22.2 22.1 Part D Trial #1 22.2 21.9 22.1 Part D Trial #2 22.0 21.9 22.0 Table #2 Temperature Recorded Every 1 Second Temperature (°C) Time Part A Part A Part B Part B Part C Part C Part D Part D (s) Trial #1 Trial #2 Trial #1 Trial #2 Trial #1 Trial #2 Trial #1 Trial #2 1 29.2 30.1 26.5 30.1 23.2 22.9 25.9 30.1 2 30.1 32 28.9 32.1 25.1 24.6 28.6 32.1 3 30.8 35.6 31.2 33.8 26.7 25.8 29.1 33.8 4 36.0 35.8 35.8 30.1 Table #3 Temperature Recorded Every 10 Seconds Temperature (°C) Time Part A Part A Part B Part B Part C Part C Part D Part D (s) Trial #1 Trial #2 Trial #1 Trial #2 Trial #1 Trial #2 Trial #1 Trial #2 10 34.5 35.8 35.8 33.8 26.6 25.4 30.1 30.9 20 34.5 35.7 34.7 33.8 26.5 25.4 30 30.9 Temperature (°C) 30 34.5 35.7 34.7 33.8 26.5 25.4 30 30.9 40 34.2 35.7 34.7 33.7 26.3 25.2 30 30.8 50 34.1 35.6 34.7 33.5 26.3 25.2 29.9 30.6 60 34.1 35.6 34.7 33.4 26.3 25.1 29.9 30.6 Table #4 Temperature Recorded Every 30 Seconds Temperature (°C) Time Part A Part A Part B Part B Part C Part C Part D Part D (s) Trial #1 Trial #2 Trial #1 Trial #2 Trial #1 Trial #2 Trial #1 Trial #2 30 34 35.6 34.7 33.3 26.3 25.2 29.9 30.6 60 33.9 35.4 34 33.3 26.3 25.1 29.8 30.4 90 33.8 35.2 33.8 33.3 26.2 25.1 29.8 30.2 120 33.1 35.1 33.7 33.2 26.2 25.1 29.8 30.2 150 33 35.1
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