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Calorimetry Lab Write-up...

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Experiment 6.

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Experiment 6. (1 week) (LCA) Calorimetry Purpose To become familiar with the principles of calorimetry by analyzing the enthalpy change of two commonplace chemical processes using a self-built calorimeter

Introduction Calorimetry is the science concerned with determining energy changes of a system by measuring heat exchange between it and its surroundings.1 A calorimeter is the device used to measure the transfer of energy out of or into the system.1 According to the first law of thermodynamics, the energy of a system can change through the transfer of heat (q) or the doing of work (w) on or by the system.2 Conventionally, q positive when heat enters the system and w is negative when the system does work, mainly by expanding.3 In a calorimeter, heat is either transferred by the system to its surroundings or absorbed from them. Therefore, assuming the process occurs at maximum efficiency, then the change in heat energy q inside the calorimeter should be 0. Therefore, the energy change from the reaction inside the calorimeter qreact should equal the change in thermal energy of the calorimeter’s components qteemp.3 qtemp is equal to the change in temperature of the calorimeter (∆T) multiplied by its heat capacity C cal, which defines the amount of energy in Joules needed to raise its temperature by 1°C. Ccal is the sum of the heat capacities of all the components of the calorimeter. For our experiments purposes, it will be assumed that only the water and inner beaker exchange heat with the reaction, making Ccal = Cwater + Cbeaker.3 Therefore, overall, the main equation that will be used for this lab is: qreact = qtemp = Ccal T

Procedure The following is an abbreviated description of the procedure. For more detail, refer to the Chem 112 First Year Lab Manual.3 Part A: Determining the Enthalpy of Dissociation of Ammonium Nitrate

1. A calorimeter, consisting of two beakers within each other, with a layer of paper towel between them, and a cardboard lid was constructed. Mass of inner beaker was measured. 2. 100ml water was added into the calorimeter. Initial temperature was measured. 3. Ammonium nitrate of measured mass was added to the calorimeter, the lid quickly closed, and final temperature measured. Part B: Determining the Enthalpy of Absorption by Sodium Polyacrylate

The same steps as Part A were repeated, but with adding sodium polyacrylate instead of ammonium nitrate.

Experiment 6.

Data and Observations Part A: Mass of inner beaker = 64.78 g Mass of ammonium nitrate = 3.01 g T1 = 20.8 °C T2 = 18.7 °C Ammonium nitrate is a white crystalline solid. When dissolved in water, it forms a colourless solution. Part B: Mass of inner beaker = 64.78 g Mass of sodium polyacrylate = 3.25 g T1 = 20.3 °C T2 = 21.4 °C Sodium polyacrylate is a white crystalline solid. Upon adding water, it absorbs it and expands significantly, forming a soft white snow-like mass.

Questions 1. Determine the heat capacity of the calorimeter used in parts A and B. Specific heat capacity of water4 = 4.186 J/g°C Specific heat capacity of Pyrex glass5 = 0.75 J/g°C Ccal for Part A & B: Ccal = 100.0 g (4.186 J/g°C) + 64.78 g (0.75 J/g°C) = 467.2 J/°C 2. Use the temperature data you collected in parts A and B to compute the enthalpies for the following reactions: a. The dissociation of ammonium nitrate in water. NH4NO3 (s) → NH4+ (aq) + NO3– (aq) m NH4NO3 = 3.01 g n NH4NO3 = 3.01 g / 80.043 g/mol = 0.0376 mol ∆T = T2 – T1 = 18.7 °C – 20.8 °C = -2.1 °C ∆H’ = q react = - Ccal ∆T = - (467.2 J/°C) (-2.1 °C) = 981.12 J ∆H = ∆H’/n = 981.12 J / 0.0376 mol = 26093.617 J/mol = 26.1 kJ/mol

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Experiment 6.

Since ∆H is positive, therefore this process is endothermic b. The absorption of water by sodium polyacrylate. ∆T = T2 – T1 = 21.4 °C – 20.3 °C = 1.1 °C m sodium polyacrylate = 3.25 g ∆H’ = q react = - Ccal ∆T = - (467.2 J/°C) (1.1 °C) = -513.92 J ∆H = -513.92 J/ 3.25 g = -158.129 J/g = -0.158 kJ/g Since ∆H is negative, therefore the process is exothermic

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Experiment 6.

References [Each reference listed here should have a number that corresponds to the superscripted number in the body of the report where this reference is pertinent.] 1. The Physics Classroom. (n.d.). Calorimeters and Calorimetry. Retrieved November 21, 2019, from https://www.physicsclassroom.com/class/thermalP/Lesson-2/Calorimeters-and-Calorimetry. 2. Libretexts. (2019, June 23). The Four Laws of Thermodynamics. Retrieved from https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/ Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Thermodynamics/The_Four_La ws_of_Thermodynamics. 3. Queen’s Chemistry, First-Year Laboratory Manual, Chemistry 112, Pages 85-90 4. Nave, R. (n.d.). Specific Heat. Retrieved November 21, 2019, from http://hyperphysics.phyastr.gsu.edu/hbase/thermo/spht.html. 5. Engineering Toolbox. (2003). Specific Heat of Solids. Retrieved November 21, 2019, from https://www.engineeringtoolbox.com/specific-heat-solids-d_154.html.

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