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Apr 30, 2024

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Endothermic vs. Exothermic In various chemical processes such as reactions and the dissolving of salts, heat is either absorbed or given off. We call these events either an endothermic (heat in) or exothermic (heat out) process. It is usual to detect these heat events by measuring the temperature change associated with the process. In this problem, you will dissolve several salts in water, measure the resulting temperature change, and then make deductions about the nature of the process. In this video we'll show you how to work with the balance to weigh out solids. 00:00 Calorimetry Lab Tips 1. To start this activity, click this link for Endothermic vs. Exothermic lab will load in a new tab. Click back to this tab to read further instructions and complete the questions below. You can follow along with the instructions below in the Procedures tab in the lab. from the list of assignments. The 2. There will be a bottle of sodium chloride (NaCl) on the lab bench. A weigh paper will be on the balance with approximately 2 g of NaCl on the paper. 3. The calorimeter will be on the lab bench and filled with 100 mL water. Make certain the stirrer is On (you should be able to see the shaft rotating). In the Thermometer section of the Live Data tray menu click Save Data to begin recording data. Allow 20-30 seconds to obtain a baseline temperature of the water. In this video we'll show you how to add salt to the calorimeter.
TBefore25 4. Drag the weigh paper with the sample to the calorimeter until it snaps into place and then pour the sample into the calorimeter. Observe the change in temperature until it reaches a minimum or maximum and then record data for an additional 20-30 seconds. (You can click on the clock on the wall labeled Accelerate to accelerate the time in the laboratory.) Click Stop Saving. Open the Lab Book menu in the tray. Record the temperature before adding the NaCl and the highest or lowest temperature after adding the NaCl below. TAfer 24.79 00:00 TBefore 25 5. Click the red disposal bucket or the Clear Lab button to clear the lab. Open the Presets menu in the tray and select the preset experiment called Heat of Solution-NaNO, and repeat the experiment with NaNO. Record the initial and final temperatures below. Calorimetry Lab Tips T ner23.95 TBefore 25 6. Click the red disposal bucket or the Clear Lab button to clear the lab. Open the Presets menu in the tray and select the preset experiment called Heat of Solution-NaAc and repeat the experiment with NaCH,COO (NaAc). Record the initial and final temperatures below. T Rer- 25.98
7. 4T NaC= -0.21 Calculate 4T (4T= TAfer-TBefore) for each mixture and record it below. 4T NaNO,= 1.05 4T NaCH,CO0 = 0.98 NaCl 8. An exothermic process gives off heat (warms up). An endothermic process absorbs heat (cools off). Which solutions are endothermic and which are exothermic? What is the sign of the change in enthalpy AH in each case? NaNO3 °C O slightly endothermic O- AH O+ AH O+ AH O- AH NaCH,C00 °C O exothermic Oendothermic Oexothermic + AH O slightly exothermic O- AH endothermic
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9. NaCI Which solution(s) had little or no change in temperature?
3-2: Enthalpy of Solution: NH4NO3 Have you ever used one of those "instant cold packs" that looks like a plastic bag filled with liquid? If you hit the bag and shake it up it gets extremely cold, but why does it do that? The liquid inside the cold pack is water, and in the water is another plastic bag or tube containing NHNO, fertilizer. When you hit the cold pack, it breaks the tube so that the water mixes with the fertilizer. The dissolving of a salt, such as NHNO3, in water is called dissolution, and the heat associated with the dissolving process is called the Enthalpy of Solution. In this problem, you will take a sample of NH,NO3, dissolve it in water, and after measuring the change in temperature, calculate the enthalpy of solution for NH NO3. In this video we'll show you how to work with the balance to weigh out solids. 00:54 Clhck back to th1s tab to read turther instructions and complete the questions below. You can tollow along with the instructions below in the Procedures tab in the lab. 2. There will be a bottle of ammonium nitrate (NH,NO;) On the lab bench. A weigh paper will be on the balance with approximately 2 g of NH,NO, on the paper. Record the mass of the sample below. If you cannot read the mass on the balance, click in the balance area to zoom in. Mass NHNO= 1.9988
3. The coffee cup calorimeter will be on the lab bench and filled with 100 mL water. Make certain the stirrer Tinitial 25 is On (you should be able to see the shaft rotating). In the Thermometer section of the Live Data tray menu click Save Data to begin recording data. Allow 20-30 seconds to obtain a baseline temperature of the water. 5. In this video we'Il show you how to add salt to the calorimeter. 00:24 -1.36 °C 4. Drag the weigh paper with the sample to the calorimeter until it snaps into place and then pour the sample into the calorimeter. Observe the change in temperature until it reaches a maximum or minimum and then record data for an additional 20-30 seconds. (You can click on the clock on the wall labeled Accelerate to accelerate the time in the laboratory.) Click Stop Saving. Open the Lab Book menu in the tray and record the highest or lowest temperature after adding the NHNO3. Tinal 23.64 °C Calculate A T(AT= Tâna!- T;nitia) for the dissolvingprocess. °C
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6. An exothermic process gives off heat (warms up), and an endothermic process absorbs heat (cools off). Was the addition of NHNO, to the water an endothermic or exothermic process? O exothermic endothermic What is the sign of the change in enthalpy AH? O+ AH O-AH 7. Determine the moles of NH4NO, in the sample. The molecular weight of NH,NO, is 80 g/mol. 0.024986 mol NHÊNO3 8. The heat absorbed or lost by the water can be calculated using q-myater CwaterAT. Assume that the density of water is 1 g/mL. Calculate the mass of the water. A Tis the change in the temperature of the water and Cwater is the specific heat capacity for water (4.184 J/gK). What is the heat absorbed or lost, in J, by the water? -5.69024 J 9. The heat transferred from/to the NH,NO; can be divided by the moles of NH,NO, to obtain the molar heat of solution for NH,NO,. Remember to use the absolute value of the Q transferred. What is the molar heat of solution, in kJ/mol, of NHNO;? 227.7371 kJ/mol
10. 786.48 If the accepted value for the heat of solution for NHNO; is 25.69 kJ/mol, calculate the percent error. % % Error |your answer-accepted answer accepted answer 100 This experiment does not consider that all of the conditions are standard state conditions; therefore, you are calculating AHsoi not 4H° sol

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