Exam (elaborations) GIZMOS Feel the Heat

Exam (elaborations) GIZMOS Feel the Heat Vocabulary: calorimeter, conductor, controlled experiment, dissolve, endothermic, exothermic, insulator, solute, solution, solvent, surroundings, system Prior Knowledge Questions (Do these BEFORE using the Gizmo.) [Note: The purpose of these questions is to activate prior knowledge and get students thinking. Students are not expected to know the answers to the Prior Knowledge Questions.] Eduardo hurts his knee during a basketball game. The trainer applies a cold pack, which gets cold after being squeezed. The next day, Eduardo’s friend Beth is going sledding. Beth buys some hand warmers and puts them into her gloves. All morning, her hands stay toasty warm. 1. How do you think these devices work? Answers will vary. [Cold packs typically work by dissolving a salt such as ammonium nitrate into water. Commercial hot packs work by crystalizing sodium acetate or by oxidizing iron.] 2. Where do you think the “cold” and the heat comes from? Answers will vary. Gizmo Warm-up As you saw with the instant cold pack and the hand warmers, some reactions absorb energy while others release it. In the Feel the Heat Gizmo, you will explore these energy changes while making your own hot and cold packs. To begin, select the TEST POWDERS tab. Drag a bottle of NaC2H3O2 (sodium acetate) from the shelf. Using the sliders, decide how much water and powder to add. Note the beginning temperature, and then press Play ( ) to see what happens. 1. Did the temperature go up or down? Up 2. Experiment with different powders until you find one that produces the opposite effect. What powder did you use? NH4NO3, KCl, and NaCl will produce a temperature decrease. When a powder dissolves in water a solution is formed. The powder is the solute and the water is the solvent. Oftentimes energy changes accompany the formation of a solution. When added to water, some powders cause the resulting solution to get hot, while others make it cold. Some powders don’t produce a temperature change at all. When energy changes do occur, they can be put to good use. This study source was downloaded by from CourseH on :40:29 GMT -05:00 This study resource was shared via CourseH GIZMOS Feel the Heat 2019 Activity A: Molecular view Get the Gizmo ready:  Click Reset ( ).  Drag a bottle of NaC2H3O2 from the shelf. Introduction: The reactions in this activity are performed within a calorimeter, an insulated device that keeps heat from escaping, enabling you to accurately record temperature changes. Question: Why does the temperature change when a powder is dissolved in water? 1. Observe: Turn on Show molecular view, and notice the water molecules. Set the Water volume to 100 mL and the Powder mass to 20 g, and then click Play. Click Pause ( ) after adding the powder. You should now see show some sodium acetate in the water. A. What color represents the bonds between the particles of NaC2H3O2? Orange B. Click Play. Watch the animation a few times. What happens to the NaC2H3O2 bonds? They are broken. C. What happens to the bonds between water molecules? They are broken. D. What color are the new bonds that form between the solute and solvent? Blue 2. Investigate: In the animation, the purple arrows represent energy that is being absorbed from the water, while the orange arrows show energy that is being released into the solution. A. Replay the animation, carefully noting the purple arrows. What does this absorbed energy do? The absorbed energy breaks apart bonds between the solute particles. B. Now replay the animation but focus on the orange arrows. What occurs every time an orange arrow is released? New bonds are formed between solute and solvent. C. Fill in the blanks: When bonds are broken, energy is absorbed. When new bonds form, energy is released. D. Based on the arrow sizes, do you think more energy is absorbed in breaking bonds, or is more energy released when new bonds form? More energy is released. E. Which bonds do you think are stronger, the bonds that are broken or the bonds that are formed? Explain your reasoning. The bonds that are formed are stronger. Since more energy is released as a result of bond formation than is absorbed to break bonds, the bonds formed must be stronger. (Activity A continued on next page) This study source was downloaded by from CourseH on :40:29 GMT -05:00 This study resource was shared via CourseH 2019 Activity A (continued from previous page) 3. Infer: Drag a bottle of KCl from the shelf. Add 20 g of water to 100 mL of water. Click Play and look once again at the molecular view. A. Did the temperature rise or fall? Fall B. Compare the purple and orange arrows. Does more energy go into breaking bonds, or is more energy released when new bonds form? Breaking bonds C. Which bonds are stronger: the bonds formed or the bonds broken? Broken Explain your reasoning. Since more energy is absorbed than released, then the bonds that are broken must be stronger than the bonds that are formed. 4. Think and discuss: Based on your observations, why do you think the temperature of the NaC2H3O2 solution rose while that of the KCl solution fell? For NaC2H3O2, the formed bonds were stronger than the broken bonds, so more energy was released than absorbed. For KCl, broken bonds were stronger, so more heat was absorbed. 5. Think and discuss: If a solute has really strong bonds between its particles, would you expect it to form a solution that gets hold or cold? Explain your reasoning. The solution will probably get cold. Breaking the strong solute bonds will require absorbing a large amount of energy, so it is likely that more energy will be absorbed than released. 6. Infer: Some powders produce little to no temperature change when added to water. Find the powder that has the smallest effect on the temperature of the resulting solution. A. What is the identity of this powder? NaBr B. How do the purple and orange arrows compare? They are roughly the same size. C. For this powder, how do you think the strength of the bonds that are broken compare to those that are formed? The broken bonds and formed bonds are equally strong. 7. Predict: Set the water to 200 mL and the powder to 1 g. Test each powder, looking only at the molecular view each time. After carefully observing the arrows, predict the following. Which powder do you think will produce the hottest solution? Answers will vary. [CaCl2] Which powder do you think will produce the coldest solution? Answers will vary. [NH4NO3] This study source was downloaded by from CourseH on :40:29 GMT -05:00 This study resource was shared via Course