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    Topic: Heating Curves Calculation Of Heat

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    Heating Curves Calculation Of Heat
    1

    What is the total amount of heat required to vaporize 1.00 gram of H2O(ℓ) at 100.°C and 1 atmosphere?

    (1) 4.18 J

    (2) 334 J

    (3) 373 J

    (4) 2260 J

    2

    A gas changes directly to a solid during

    (1) fusion

    (2) deposition

    (3) saponification

    (4) decomposition

    3

    Given the cooling curve of a substance:

    physical-behavior-of-matter, heating-curves-calculation-of-heat, physical-behavior-of-matter, heat-and-temperature, physical-behavior-of-matter, heat-and-temperature fig: chem12013-exam_g4.png

    During which intervals is potential energy decreasing and average kinetic energy remaining constant?

    (1) AB and BC

    (2) AB and CD

    (3) DE and BC

    (4) DE and EF

    4

    The graph below represents the relationship between time and temperature as heat is added at a constant rate to a sample of a substance.

    physical-behavior-of-matter, heating-curves-calculation-of-heat, physical-behavior-of-matter, heat-and-temperature fig: chem12014-exam_g6.png

    During interval AB, which energy change occurs for the particles in this sample?

    (1) The potential energy of the particles increases.

    (2) The potential energy of the particles decreases.

    (3) The average kinetic energy of the particles increases.

    (4) The average kinetic energy of the particles decreases.

    5

    What is the amount of heat energy released when 50.0 grams of water is cooled from 20.0°C to 10.0°C?

    (1) 5.00 × 102 J

    (2) 2.09 × 103 J

    (3) 1.67 × 105 J

    (4) 1.13 × 106 J

    6

    At 101.3 kPa and 298 K, a 1.0-mole sample of which compound absorbs the greatest amount of heat as the entire sample dissolves in water?

    (1) LiBr

    (2) NaCl

    (3) NaOH

    (4) NH4Cl

    7

    A 100.-gram sample of H2O(ℓ) at 22.0°C absorbs 8360 joules of heat. What will be the final temperature of the water?

    (1) 18.3°C

    (2) 20.0°C

    (3) 25.7°C

    (4) 42.0°C

    8

    The heating curve below represents a sample of a substance starting as a solid below its melting point and being heated over a period of time.

    physical-behavior-of-matter, heating-curves-calculation-of-heat, physical-behavior-of-matter, heat-and-temperature fig: chem12016-exam_g3.png

    Which statement describes the energy of the particles in this sample during interval DE?

    (1) Both potential energy and average kinetic energy increase.

    (2) Both potential energy and average kinetic energy decrease.

    (3) Potential energy increases and average kinetic energy remains the same.

    (4) Potential energy remains the same and average kinetic energy increases.

    Base your answers to questions 9 on the information below and on your knowledge of chemistry.

    A beaker contains a liquid sample of a molecular substance. Both the beaker and the liquid are at 194 K. The graph below represents the relationship between temperature and time as the beaker and its contents are cooled for 12 minutes in a refrigerated chamber.

    physical-behavior-of-matter, heat-and-temperature, physical-behavior-of-matter, heat-and-temperature fig: chem82016-exam_g12.png

    9

    Identify the physical change occurring during the time interval, minute 4 to minute 9.

    Allow 1 credit. Acceptable responses include, but are not limited to:

    • freezing

    • solidification

    • liquid to solid

    Base your answers to questions 10 on the information below.

    A student investigated heat transfer using a bottle of water. The student placed the bottle in a room at 20.5°C. The student measured the temperature of the water in the bottle at 7 a.m. and again at 3 p.m. The data from the investigation are shown in the table below.

    physical-behavior-of-matter, heat-and-temperature fig: chem12013-exam_g21.png

    10

    Show a numerical setup for calculating the change in the thermal energy of the water in the bottle from 7 a.m. to 3 p.m.

    Allow 1 credit. Acceptable responses include, but are not limited to:

    • q = (800. g)(4.18 J/g•°C)(20.5°C − 12.5°C)

    • (800)(4.18)(8)

    Base your answers to questions 11 on the information below and on your knowledge of chemistry.

    The formulas and the boiling points at standard pressure for ethane, methane, methanol, and water are shown in the table below.

    physical-behavior-of-matter, intermolecular-forces-and-physical-properties-of-substances fig: chem12015-exam_g16.png

    11

    State the change in potential energy that takes place in a sample of methane as it boils at −161.5°C.

    Allow 1 credit. Acceptable responses include, but are not limited to:

    • As liquid methane boils, the potential energy of the sample increases.

    • Potential energy increases.

    Base your answers to questions 12 on the information below and on your knowledge of chemistry.

    A student made a copper bracelet by hammering a small copper bar into the desired shape. The bracelet has a mass of 30.1 grams and was at a temperature of 21°C in the classroom. After the student wore the bracelet, the bracelet reached a temperature of 33°C. Later, the student removed the bracelet and placed it on a desk at home, where it cooled from 33°C to 19°C. The specific heat capacity of copper is 0.385 J/g•K.

    12

    Show a numerical setup for calculating the amount of heat released by the bracelet as it cooled on the desk.

    Allow 1 credit. Acceptable responses include, but are not limited to:

    • q = (30.1 g)(0.385 J/g•K)(19°C − 33°C)

    • (30.1 g)(306 K − 292 K)(0.385 J/g•K)

    • (0.385)(30.1)(14)

    Base your answers to questions 13 on the information below and on your knowledge of chemistry.

    Seawater contains dissolved salts in the form of ions. Some of the ions found in seawater are Ca2+, Mg2+, K+, Na+, Cl−, HCO3−, and SO42−. An investigation was conducted to determine the concentration of dissolved salts in seawater at one location. A 300.-gram sample of the seawater was placed in an open container. After a week, all the water had evaporated and 10. grams of solid salts remained in the container.

    13

    Explain why the evaporation that occurred during the investigation is an endothermic process.

    Allow 1 credit. Acceptable responses include, but are not limited to:

    • Energy is needed to overcome the intermolecular forces.

    • Energy is required to change liquid water to water vapor.

    • The heat of vaporization is positive.

    Base your answers to questions 14 on the information below and on your knowledge of chemistry.

    Carbon dioxide, CO2, changes from the solid phase to the gas phase at 1 atm and 194.5 K. In the solid phase, CO2 is often called dry ice. When dry ice sublimes in air at 298 K, the water vapor in the air can condense, forming a fog of small water droplets. This fog is often used for special effects at concerts and in movie-making.

    14

    At 1 atm and 298 K, compare the potential energies of the water molecules before and after the water vapor condenses.

    Allow 1 credit. Acceptable responses include, but are not limited to:

    • The potential energy of the H2O(g) molecules is higher than the potential energy of the H2O(ℓ) molecules.

    • The water vapor has greater PE.

    • There is less PE in the liquid water.

    15

    Show a numerical setup for calculating the quantity of heat in joules required to completely vaporize 102.3 grams of H2O(ℓ) at 100.°C and 1.0 atm.

    Allow 1 credit. Acceptable responses include, but are not limited to:

    • q = (102.3 g)(2260 J/g)