AP Chem 6.1-6.4 Assignment

Question 5 A 10.0mL sample of 1.0M AgNO3(aq) and a 10.0mL sample of 1.0MNaBr(aq), both originally at 25°C, are combined in a constant-pressure calorimeter where the reaction represented above occurs. If the final temperature of the mixture is 35°C, what is the value of ΔH for the reaction? (Assume that the heat absorbed by the calorimeter is negligible, that the total mass of the mixture is 20.0g, and that the specific heat capacity of the mixture is 4.2J/(g·°C).

A. -84,000 J/mol

Question 16 A student adds 50.0g of liquid water at 25.0°C to an insulated container fitted with a temperature probe. The student then adds 10.0g of ice at 0.0°C, closes the container, and measures the temperature at different intervals. Part of the data is shown in the graph above. The student predicts that the temperature will continue to decrease then level out to a constant temperature. Which of the following best explains why the student's prediction is correct?

A. The H2O molecules initially in the ice and the molecules initially in the liquid will have the same average kinetic energy.

Question 10 The heating curve for a sample of pure ethanol is provided above. The temperature was recorded as a 50.0 g sample of solid ethanol was heated at a constant rate. Which of the following explains why the slope of segment T is greater than the slope of segment R? Responses

A. The specific heat capacity of the gaseous ethanol is less than the specific heat capacity of liquid ethanol.

Question 17 XY2 → X + Y2 The equation above represents the decomposition of a compound XY2. The diagram below shows two reaction profiles (path one and path two) for the decomposition of XY2. Which of the following best describes the flow of heat when 1.0 mol of XY2 decomposes?

B. 50 kJ of heat is transferred from the surroundings.

Question 18 The elements K and Cl react directly to form the compound KCl according to the equation above. Refer to the information above and the table below to answer the questions that follow. Which of the values of ΔH° for a process in the table is (are) less than zero (i.e., indicate(s) an exothermic process) ?

B. y and z only

Question 6 Samples of Fe and Al are heated from 25∘C to 75∘C. Based on the information in the table above, the change in the average kinetic energy of the atoms in the samples is

C. the same for both metal samples, because the initial and final temperatures are the same

Question 3 A 1.0 g sample of a cashew was burned in a calorimeter containing 1000. g of water, and the temperature of the water changed from 20.0°C to 25.0°C. In another experiment, a 3.0 g sample of a marshmallow was burned in a calorimeter containing 2000. g of water, and the temperature of the water changed from 25.0°C to 30.0°C. Based on the data, which of the following can be concluded about the energy content for 1.0 g of each of the two substances? (The specific heat of water is 4.2 J/(g⋅°C).)

C. The combustion of 1.0 g of cashew releases more energy than the combustion of 1.0 g of marshmallow.

Question 14 For an experiment, 50.0g of H2O was added to a coffee-cup calorimeter, as shown in the diagram above. The initial temperature of the H2O was 22.0°C, and it absorbed 300.J of heat from an object that was carefully placed inside the calorimeter. Assuming no heat is transferred to the surroundings, which of the following was the approximate temperature of the H2O after thermal equilibrium was reached? Assume that the specific heat capacity of H2O is 4.2J/(g⋅K).

D. 23.4 C

Question 15 A piece of Fe(s) at 25°C is placed into H2O(l) at 75°C in an insulated container. A student predicts that when thermal equilibrium is reached, the Fe atoms, being more massive than the H2O molecules, will have a higher average kinetic energy than the H2O molecules. Which of the following best explains why the student's prediction is incorrect?

D. At thermal equilibrium, the average kinetic energy of the Fe atoms cannot be greater than that of the H2O molecules; the average kinetic energies must be the same according to the definition of thermal equilibrium.

Question 13 A student was given samples of four different unknown liquids. The unknown liquids are propylamine, pentane, 2-propanol, and propanoic acid. The structures and molar masses of the compounds are shown in the table above. On the basis of this information, the student designed some experiments to identify the samples. Which of the following statements correctly identifies which compound, pentane or propanoic acid, has the higher boiling point and provides a valid justification?

D. Propanoic acid, because it forms hydrogen bonds, whereas pentane does not

Question 12 In the spring, blossoms on cherry trees can be damaged when temperatures fall below −2°C. When the forecast calls for air temperatures to be below −5°C for a few hours one night, a farmer sprays his blossoming cherry trees with water, claiming that the blossoms will be protected by the water as it freezes. Which of the following is a correct scientific justification for spraying water on the blossoms to protect them from temperatures below −2°C?

D. The freezing of water is an exothermic process; thus, water that freezes on the blossoms releases heat to keep the blossoms at or above −2°C.

Question 11 In an insulated cup of negligible heat capacity, 50. g of water at 40.°C is mixed with 30. g of water at 20.°C. The final temperature of the mixture is closest to

D. 33 C

Question 2 For a classroom demonstration, a chemistry teacher puts samples of two different pure solid powders in a beaker. The teacher places the beaker on a small wooden board with a wet surface, then stirs the contents of the beaker. After a short time the students observe that the bottom of the beaker is frozen to the wood surface. The teacher asks the students to make a claim about the observation and to justify their claims. Which of the following is the best claim and justification based on the students' observation?

D. An endothermic chemical change occurred because the temperature of the beaker and the water on the board decreased as heat was absorbed by the reaction.

Question 1 A quantity of 10,000 J of thermal energy is transferred to four different substances. In which of the following experiments could the greatest mass of the given substance undergo the indicated change?

Increasing the temperature of solid copper from 0.°C to 200.°C(Specific heat = 0.40 J/(g x C))

Question 7 A 100g sample of a metal was heated to 100oC and then quickly transferred to an insulated container holding 100g of water at 22oC. The temperature of the water rose to reach a final temperature of 35oC. Which of the following can be concluded? Responses

The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained.

Question 8 A 100 g sample of a metal was heated to 100oC and then quickly transferred to an insulated container holding 100 g of water at 22oC. The temperature of the water rose to reach a final temperature of 35oC. Which of the following can be concluded? Responses

The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained.

Question 4 NaOH(aq) + HCl(aq) → H2O(l) + NaCl(aq) A student is trying to determine the heat of reaction for the acid-base neutralization reaction represented above. The student uses 0.50 M NaOH and 0.50 M HCl solutions. Which of the following situations, by itself, would most likely result in the LEAST error in the calculated value of the heat of reaction?

The thermometer was incorrectly calibrated and read 0.5 Celsius degree too high during the procedure.

Question 9 A 30.g sample of Al(s)is heated to 50°C and placed in a calorimeter containing 150g of water at 20°C. As the system approaches thermal equilibrium, energy is transferred

from the Al(s) to the water and the temperature of the Al(s) decreases