Energy Review 1. Which phase change results in the release of energy? (1) H20(s)_>H20(4 (3) H20«)->H20(g) (2) H20(s)-»H20(g) (4) H20(g)-*H20«2. The burning of magnesium involves a conversion of (1) chemical energy to mechanical energy (2) chemical energy to heat energy (3) heat energy to chemical energy (4) heat energy to mechanical energy 3. Which term represents a form of energy? (1) heat (3) kilocalorie (2) degree (4) temperature 4. The energy absorbed when ammonium chloride dissolves in water can be measured in (1) degrees (3) parts per million (2) kilojoules (4) liters per mole 5. The potential energy possessed by a molecule is dependent upon (1) its composition, only (2) its structure, only (3) both its composition and its structure (4) neither its composition nor its structure 11. A liquid's freezing point is -38 C and its boiling point is 357 C. What is the number of Kelvin between the boiling point and the freezing point of the liquid? (1) 319 (3) 592 (2) 395 (4) 668 12. Which physical changes are endothermic? (1) melting and freezing (2) melting and evaporating (3) condensation and sublimation (4) condensation and deposition 13. As a solid is heated, its temperature increases from 10 C to 25 C, remains at 25 C for 5 minutes, and then increases to beyond 45 C. Based on this information, what conclusion can be drawn about the substance? (1) ts melting point is 45 C. (3) ts melting point is 25 C. (2) ts boiling point is 45 C. (4) ts boiling point is 25 C. 14. Base your answer to the following question on the graph below, which represents uniform cooling of a sample of a pure substance, starting as a gas. 180 6. As electrical energy is converted into heat energy, the total amount of energy in the system (1) decreases (3) remains the same (2) increases 7. The average kinetic energy of the molecules of an ideal gas is directly proportional to the (1) number of moles present (2) volume oupied by individual gas molecules (3) temperature measured on the Kelvin scale (4) pressure at standard temperature 120 60 ife Time in Minutes 8. At which temperature would the molecules in a one gram sample of water have the lowest average kinetic energy? (1) 5 C (3) 5K (2) -100 C (4) 100K Solid and liquid phases can exist in equilibrium between points (1) andf (3) CandZ) (2) flandc (4) DandE 9. Solid^ at 80 C is immersed in liquid B at 60 C. Which statement correctly describes the energy changes between A and 5? (1) A releases heat and B absorbs heat. (2) A absorbs heat and B releases heat. (3) Both A and B absorb heat. (4) Both A and B release heat. 10. The temperature 30. K expressed in degrees Celsius is (1) 243 C (3) 303 C (2) -243 C (4) -303 C Pagel
15. Which graph best represents a change of phase from a gas to a solid? (1) (2) a. Q. TME TME (3) (4) jjj* Q. Ul CL TME TME 22. The graph below shows the relationship between vapor pressure and temperature for substance X. To 2- «1.0? 0.5 ^ S n -" X > 10 20 30 40 50 Temperature ( C) What is the normal boiling point for substance X? (1) 50 C (3) 30 C (2) 20 C (4) 40 C 16. When 200 grams of water cools from 50. C to 25 C, the total amount of heat energy released by the water is (1) 42 kj (3) 34 J (2) 21 kj (4) 17 J 17. When 420 Joules of heat energy is added to 10. grams of water at 20. C, the final temperature of the water will be (1) 10. C (3) 40. C (2) 30. C (4) 100 C 18. How much heat energy must be absorbed to completely melt 35.0 grams of H2O(s) at 0 C? (1) 9.54 J (3) 11 700 J (2) 146 J (4) 79 100 J 19. What ours when a substance melts? (1) t changes from solid to liquid, and heat is absorbed. (2) t changes from solid to liquid, and heat is released. (3) t changes from liquid to solid, and heat is absorbed. (4) t changes from liquid to solid, and heat is released. 20. The strongest intermolecular forces of attraction exist in a liquid whose heat of vaporization is (1) 100 Jg (3) 300 Jg (2) 200 Jg (4) 400 Jg 21. How much energy is required to vaporize 10.00 grams of water at its boiling point? (1) 2.26 kj (3) 4.2 kj (2) 3.34 kj (4) 22.6 kj Page 2
23. Base your answers to the following questions on the information below. Often special effects technicians at rock concerts use solid carbon dioxide, "dry ice", to create a fog-like appearance on stage. The solid carbon dioxide (CO2) undergoes a phase change directly to the gaseous state, absorbing energy from the surrounding air. a Write the equation showing the phase change process undergone by the C02(s). nclude the energy term. b s this phase change of CO2 exothermic or endothermic? c What is the name of the process where a solid goes directly to a gas? 24. Given the graph below that represents the uniform cooling of a sample of lauric acid starting as a liquid above freezing point. Cooling Curve for Lauric Acid > k 70-60- o" Q 1 <DQ. 50-40- 30- \ C ^^^^^^ ^^--^D ^^* E 0) F 20-10- 0-1 [ 01 2 3 4 5 6 7 8 910 W Time (min) a Which line segment represents a phase change, only?_ b What is the melting point of lauric acid?_ c At which point do the particles of lauric acid have the highest average kinetic energy? c?name the phase change that takes place during this 10-minute cooling time. 25. a Calculate the heat released when 25.0 grams of water freezes at 0 C. Show all work. b Record your answer with an appropriate unit. Page 3
Base your answers to questions 26 through 29 on the information below. Figure 1 Figure 2 50.0 g Cu(s) at 100.0 C 100.0 g H2O(l) at 23.2 C A Styrofoam cup with a lid is used as a calorimeter. The cup contains 100.0 grams of distilled water at 23.2 C. n a laboratory investigation, a 50.0-gram sample of copper is at 100.0 C in a boiling water bath. Figure 3 Figure 4 The hot copper is poured into the cup of water, and the cup is quickly covered with the lid. A thermometer is inserted through the lid. The copper and water are gently stirred in the cup. The temperature is checked periodically. The highest temperature noted is 26.3 C. Data Table Quantity Measured Mass of copper Temperature of hot copper Mass of H2O in calorimeter nitial temperature of H2O in calorimeter Final temperature of H2O and copper Data (units are given) g C 9 C c 26. n terms of energy flow,explain why the temperature of the water in the calorimeter increases. 27. Using the information given, complete the data table above. Page 4
28. n the space below show a correct numerical setup for calculating the number of joules of heat gained by the water. 29. n this investigation, the change in heat of the copper is greater than the change in heat of the water. What error could aount for this apparent violation of the Law of Conservation of Energy? Do not use human error as part of the answer. 30. Base your answer to the following question on the information below. Given the equation for the dissolving of sodium chloride in water: TT ~\) 2 ^ Na+(aq) + CJ-(aq) When NaCl(s) is added to water in a 250-milliliter beaker, the temperature of the mixture is lower than the original temperature of the water. Describe this observation in terms of heat flow. PageS