Eliza Romanowski Partner: Diana Zuniga Shlomo Small 1 May 2017 Calorimetery and Thermochemistry “ Stealing Joules ” Introduction Scientists determine the change in thermodynamic quantities (enthalpy H, entropy S, and free energy G) using a device known as a calorimeter. The name calorimeter is derived from calorie (which is the English unit for energy) and meter (measuring device). The calorimeter is usually an insulated container that prevents heat from entering or leaving it and can be constructed from a coffee cup. Coffee cup calorimeters are used to measure changes that take place in the solution. The insulation provided by the Styrofoam cup ensures that heat is transferred only between the system (a reaction or a hot object) and the surroundings inside the cup (pure water or a solution). For example, if a reaction releases heat, the surrounding solution absorbs it and becomes hotter. Using a thermometer, we can measure the change in temperature. We know that any heat lost by the system must be absorbed by the surroundings (First Law of Thermodynamics): -qsystem = qsurroundings. Using the measured change in temperature and the heat capacity of the solution (or pure water) in the coffee cup, we can calculate the heat lost by the system. Since the experiment is performed under constant atmospheric pressure, the heat of a reaction is equal to its enthalpy change. Materials -2 Styrofoam Cup -Thermometer -Lid -HCl -NaOH -Tap Water -Cold Water -NH 4 Cl Procedure Part 1 1) Add 50.0mL of 2.0M HCl to the calorimeter and obtain the mass of calorimeter + acid. 2) Record the temperature of the acid in the calorimeter. 3) Quickly add 50.0mL of 2.0M NaOH, cover it with the lid, mix by gently swirling the cup, and start to record the temperature of the reaction mixture every 30 seconds (using a timer) until the temperature remains constant. Mix the solution from time to time. 4) Obtain the mass of calorimeter + acid + base. 5) Plot the temperature-time data, perform a linear fit for the data points obtained after combining the reactants, and determine T. 6) Calculate the heat of neutralization for a strong acid/strong base reaction. Mass of coffee cup calorimeter = 8.83g Mass of calorimeter + 50mL 2.0M HCl = 91.28g
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