Energy and chem rxn 2022 Prachi Patel

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Purdue University *

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112

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Chemistry

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Dec 6, 2023

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CHM 11100 Activities and Explorations: 10 points, Due November 20 at 11:59 PM Claim, Evidence, Reasoning (CER) – Energy and chemical reactions Instructions: Upload your work on this page to Brightspace by typing or writing your responses and saving the file as a pdf file with your first and last name and uploading that file. You can also take pictures of your written work and paste them in! Only use the PDF format, don’t use Pages, HEIC, or docx! Learning Objectives 6.1-6.2: Energy and Energy changes in chemical reactions  Distinguish between exothermic and endothermic reactions.  Describe the factors that affect the amount of heat change for a process. 6.5 Calorimetry  Use quantitative relationships related to energy including specific heat and calorimetry. Question : How does the amount of energy released (the heat change) vary per gram and per mole between two experiments for calcium chloride? In this CER activity you will need to complete a data table. The claims are given to you. Data and Observations : A team of students recorded the following data by dissolving a known mass of CaCl 2 in 100.0 mL of water. They noticed that the temperature increased for each sample (data not shown, but reflected in the negative sign for the q system ). They went on to calculate q system , the heat change for the dissolution of each sample. 1. (2 pts.) Complete the table below and show your work . The molar mass for CaCl 2 is 110.98 g/mole. Be sure to get your answer in the correct units! Data and calculations Sample CaCl 2 Mass CaCl 2 (g) Calculated q system , heat change for the dissolution (J) Heat change per mole CaCl 2 (kJ/mol) Sample #1 1.142 -824 -80.0 Sample #2 2.803 -2050 -81.3

CHM 11100 Claim A: The amount of energy released increases with the amount of CaCl 2 dissolved. Claim B: The heat change per mole is nearly constant between the two experiments. (Yes, we’ve provided both claims.) 2. (2 pts.) What evidence do you have from the data table and description of the experiment that could be used to help support the claims? Describe at least 2 pieces of evidence The amount of energy released does increase with the amount of CaCl 2 dissolved. At 1.142 g, the heat change (energy released) is -824 J and at 2.803 g it is -2050 J. This shows that more energy is being released because the number of heat change is becoming more negative and increase as more amount of CaCl 2 is dissolved. Another evidence is because of the

CHM 11100 energy being released more is because of the temperature increasing. If the temperature increases, the heat change will become more negative. The description of the experiment even claimed that they noticed that the temperature increased for each sample. 3. Reasoning to support Claim A: Connect your evidence to Claim A .  (2 pts.) Define the system & surroundings  (1 pt) Discuss how heat flows in this chemical system (to the surroundings from the system, or to the system from the surroundings – how do you know?) based upon the data table and the description of the experiment. You can draw a picture if that helps!  (1 pt) Use the data in the table to help you support your claim! The system would be the CaCl 2 dissolved in water. The surrounding would be everything around it, including the atmosphere and beaker the CaCl 2 was dissolved in. The heat flow is system to its surrounding. From the data I know the heat flow is exothermic going from the system to the surrounding because heat change is negative. If the heat change is negative, it is exothermic and energy is being released. 4. Reasoning Claim B: Connect your evidence – the data table - to your claim.  (2 pts) Use the values you found to fill out the table to support Claim B. The heat change per mole is nearly constant between the two experiments. After I found my values for heat change per mole CaCl 2, the number for sample 1 was -80.0 kJ/mol and the number for sample 2 was -81.3 kJ/mol. As you can see, the number for really close to each other which can support claim B.

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