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Lesson 8 Energy in Chemical Reactions Review

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Lesson 8 Energy in Chemical Reactions Review Name __________________________________________________ Date ______________________________ Lesson 8 Energy in Chemical Reactions Review Main Ideas Read each item. Then select the letter next to the best answer. 1. An ice pack is activated and placed on a person’s wrist. After the resulting chemical reaction, the average temperature of the hands-icepack system is lower. Which of the following statements best completes a statement about the transfer of energy in this chemical reaction. This reaction is: A. endothermic, because more thermal energy is absorbed than released. B. endothermic, because more thermal energy is released than absorbed. C. exothermic, because more thermal energy is absorbed than released. D. exothermic, because more thermal energy is released than absorbed. 2. Calcium ammonium nitrate is a chemical used in fertilizers. It can also be used to make an instant ice-pack. When the calcium ammonium nitrate is allowed to mix with the water inside the ice pack, a chemical reaction takes place. This reaction cannot occur on its own because it needs a source of heat to continue until it is complete. Which statement best describes the type of chemical reaction and the source of heat? A. Endothermic reaction, and the heat comes out of the water. B. Exothermic reaction, and the heat comes out of the water. C. Exothermic reaction, and the heat comes out of the reaction. D. Endothermic reaction, and the heat comes out of the reaction. 3. When a candle burns, a chemical reaction occurs changing wax and oxygen into carbon dioxide and water vapor. The average temperature of the candle-room system increases. Which of the following statements best completes a statement about the transfer of energy in this chemical reaction. This reaction is: A. endothermic, because more thermal energy is absorbed than released. B. endothermic, because more thermal energy is released than absorbed. C. exothermic, because more thermal energy is absorbed than released. D. exothermic, because more thermal energy is released than absorbed. 4. Pictured below is an electrolysis device used to separate hydrogen and oxygen from water. Notice there is twice as much hydrogen as oxygen in the test tubes. The battery supplies energy to separate the gasses. Later, by burning, the gasses combined back into water vapor. Which statement best describe the flow of energy in this process? A. Electrolysis stores energy, burning stores energy. B. Electrolysis releases energy, burning stores energy. C. Electrolysis stores energy, burning releases energy. D. Electrolysis releases energy, burning releases energy. 5. To develop a hot-pack that will keep food warm throughout the day, engineers developed a model and tested it. During the testing, they recorded the temperatures the hot-pack reached, shown in the graph below. Based on the data provided in the graph, which statement best describes this chemical reaction? A. This is an exothermic reaction storing energy. B. This is an endothermic reaction storing energy. C. This is an exothermic reaction releasing energy. D. This is an endothermic reaction releasing energy. 6. Your group performed two separate chemical reactions. There was some confusion on which reaction was which because the chemicals may have been mixed up. Both reactions had an initial temperature of 20°C. You have the final temperatures as 16°C and 24°C, but you do not know which reaction had which temperature. Which reaction has a final temperature of 16°C and which had a final temperature of 24°C? Reaction 1: ammonium chloride and water: NH4Cl + H20 + energy → HCl + NH4OH Reaction 2: calcium chloride and water: CaCl2 + 2H2O → Ca(OH)2 + 2HCl + energy A. Reaction 1 is had a final temperature of 16°C and Reaction 2 had a final temperature of 24°C, because Reaction 1 is endothermic and Reaction 2 is exothermic. B. Reaction 1 had a final temperature of 16°C and Reaction 2 had a final temperature of 24°C, because Reaction 1 is exothermic and Reaction 2 is endothermic. C. Reaction 1 had a final temperature of 24°C and Reaction 2 had a final temperature of 16°C, because Reaction 1 is endothermic and Reaction 2 is exothermic. D. Reaction 1 had a final temperature of 24°C and Reaction 2 had a final temperature of 16°C, because Reaction 1 is exothermic and Reaction 2 is endothermic. Investigation A group of engineers wanted create a cold pack that could be placed in a lunch box to keep food cool. They wanted to create a drop of at least 20°C in 100 mL of water. They recorded the temperature of the water every 15 seconds, with different masses of ammonium chloride. 7. Which amount of ammonium chloride results in a greater temperature change over time? A. 10 g ammonium chloride B. 15 g ammonium chloride C. 20 g ammonium chloride D. Ammonium chloride does not result in a temperature change. 8. Which reaction meets the criteria? A. Reaction 1 B. Reaction 2 C. Reaction 3 D. None of the reactions meet the criteria. 9. What further testing should be done to determine the best solution? A. Test smaller amounts of ammonium chloride, because less ammonium chloride results in a greater temperature change. B. Test smaller amounts of ammonium chloride, because less ammonium chloride results in a smaller temperature change. C. Test larger amounts of ammonium chloride, because more ammonium chloride results in a greater temperature change. D. Test larger amounts of ammonium chloride, because more ammonium chloride results in a smaller temperature change. 10. Cooking often involves thermal energy being added to a substance. Thermal energy is added when cooking vegetables. The heat results in an reaction that breaks down substances in the vegetables. A. Identify the image as either endothermic or exothermic. B. Annotate the image with arrows showing the flow of energy C. Add energy to the appropriate side of the equation Reactant AB + Reactant CD ---> Product AD + Product CB 11. Your school is starting a community garden. There are two proposed sites. One site is shady and one site is sunny. The principal wants student input on where the new garden should be located. She wants facts, not opinions, in making her decision. The gardening committee wants you to write up the proposal. A. Where should you place the garden and why? (2pts) ____________________________________________________________________________________________ ____________________________________________________________________________________________ B. Is photosynthesis considered an endothermic or exothermic reaction? How do you know? (2pts) ____________________________________________________________________________________________ ____________________________________________________________________________________________ C. Add energy to the correct side of the chemical equation. 6CO2 + 6H2O + energy → C6H12O6 + 6O2. .
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