Calorimetry Assignment PDF

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Assignment on heat calorimeter...

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Experiment 6.

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Experiment 6. (1 week) (LCA) Calorimetry Purpose The purpose is to gain knowledge about the concepts regarding Calorimetry by examining the enthalpy change of two common chemical processes using the data taken by a calorimeter built in the lab.

Introduction1 According to the first law of thermodynamics, ΔU=q+w (Equation 26) where ΔU is the overall energy change in a system, q is the heat entering or leaving the system and w is the work done on or by the system. Since the volume of the system, the calorimeter(the inner beaker with all its content) and the pressure are held constant, ΔH=qp (Equation 27) where ΔH is the enthalpy change in the system, qp is the heat emitted or absorbed at constant pressure and no non-expansion work is done on or by the system. Two energy changes are taking place inside the calorimeter, one being the energy change from the reaction, qreact and another being the change in thermal energy, qtemp. Since it is an adiabatic process (with no heat transfer in or out of the system), the energy change in the system, qsystem= 0 = qreact+qtemp (Equation 28). The change in thermal energy can be found using the heat capacity of the system, Csystem and the change in temperature, ΔT where qtemp = CsystemΔT= [mwaterCs, water+mbeakerCs, beaker] ΔT (Equation 31) in which mwater is the mass of water used in the experiment, mbeaker is the mass of the inner Pyrex beaker, Cs, water is the specific heat capacity of water and Cs, beaker is the heat capacity of the calorimeter which needs to be found. The molar enthalpy change, ΔH’ for a reaction is ΔH’= qreact= - [mwaterCs, water+mbeakerCs, beaker] ΔT (Equation 32) which is ΔH divided by the number of moles of reaction.

Procedure2 Part A: Determining the Enthalpy of Dissociation of Ammonium Nitrate At first, the 150mL beaker used in the calorimeter is weighed on a top loading balance. Then, the calorimeter is made using the 150mL Pyrex beaker which is lined with paper towel and put inside a

Experiment 6.

250mL beaker where the paper towel acts as an insulator between the two beakers, preventing heat transfer to or from the surroundings. A stir bar is put inside the smaller beaker and the two beakers are placed on the hot plate. A cardboard lid is used to cover the top of the beakers which has a hole in it for the temperature probe to be inserted through it and held in place with the clamp and retort stand. The initial temperature of the calorimeter is then measured. Next, the Logger Pro is set up following the instructions written in the lab manual and the temperature probe attached to it for automatic graphing of the temperature of water. The calorimeter is filled with 100mL of RO water with the help of a graduated cylinder and the stir bar is switched on to 300 rpm with the temperature of water being observed to ensure it is stable. About 3.0g of ammonium nitrate crystals is measured on a top loading balance. The plot of temperature of the water inside the calorimeter is measured and collected for 30 seconds after which the crystals are added and the data collected for the remaining 300 seconds. Lastly, ΔT of the reaction is calculated from the auto scaled graph and the contents of the calorimeter are washed away to make the calorimeter again for Part B. Part B: Determining the Enthalpy of Absorption by Sodium Polyacrylate The calorimeter is again set up the same way as in Part A. The polymer, sodium polyacrylate is extracted at first following the instructions in the lab manual and then about 3.0g of it is measured on a top loading balance. 100mL of RO water is poured into the 150mL beaker using a graduated cylinder and the stir bar is turned on. The data of the temperature of the water is taken and plotted for 30 seconds after it reaches stability with the remaining data collected for 300 seconds after the polymer is added. ΔT of this reaction is found out from the auto scaled graph.

Data and Observations The initial temperature and the final temperature of the reaction in Part A were 21.1 ᵒC and 19.2ᵒC respectively with the ΔT=-1.9ᵒC. A decrease in temperature of the water was noticed from the graph drawn by the computer after the ammonium nitrate crystals were added to the water in Part A. When the solution was poured from the beaker, tiny white flakes of ammonium nitrate were seeing in the water. However, the initial and final temperatures of the reaction in Part B were 22.3ᵒC and 24.00ᵒC respectively with the ΔT=1.7ᵒC. As the diaper was ripped across the liner, small crystals of sodium polyacrylate were seen there which was dumped into the beaker slowly. There was an increase in temperature of the water after the polymer, sodium polyacrylate was added to it which absorbed water and became a solid like snow.

Questions 1. Determine the heat capacity of the calorimeter used in parts A and B. Specific Heat Capacity of water= 4.1855 g -1K-1 Specific Heat Capacity of Pyrex Glass= 0.75 g -1K-1 Ccal= CH2O + CBeaker = (100g x 4.1855 Jg -1ᵒC-1) + ( 65.96g x 0.75 Jg -1ᵒC-1) = 468 JᵒC-1 is the heat capacity of the calorimeter in Part A

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Experiment 6.

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Part B Ccal= CH2O + CBeaker = (100g x 4.1855 Jg -1ᵒC-1) + ( 65.96g x 0.75 Jg -1ᵒC-1) = 468 JᵒC-1 is the heat capacity of the calorimeter in Part B 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. [Enthalpy change per mole of ammonium] b. The absorption of water by sodium polyacrylate. [Enthalpy change per gram of sodium polyacrylate] a. NH4NO3 (s) → NH4+ (aq) + NO3- (aq) NH4NO3 m= 3.00g M= 80.06 g/mole n= 3.00/80.06= 0.0374 mole ΔHᵒrxn= (-Ccal x ΔT)/n = ( -468 JᵒC-1 x -1.9ᵒ C)/0.0374 = + 23.8 kJ/mole which is endothermic

b. C3H3NaO2 (s) + H2O (l) → C3H5NaO3 (s) C3H3NaO2 m= 3.00g M= 94.05g n= 3.00/94.05= 0.0319 mole ΔHᵒrxn = ( -Ccal x ΔT)/n = ( -468 JᵒC-1 x 1.7 ᵒ C)/0.0319 = -24.9 kJ/mole which is exothermic

Express your answers in kJ/mol (or kJ/g) and indicate whether each process is endothermic or exothermic.]

Experiment 6.

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Experiment 6.

References 1. Wu, Gang. Queen’s Chemistry First-Year laboratory Manual Chemistry 112; Queen’s University: Kingston ON, 2019-2020; p. 85-87 2. Wu, Gang. Queen’s Chemistry First-Year laboratory Manual Chemistry 112; Queen’s University: Kingston ON, 2019-2020; p. 88-89 3. https://www.coursehero.com>file, The reaction of Calorimetry

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