Unit 02: Nuclear Chemistry Review

A student has a 1g sample of each of the following compounds: NaCl, KBr, and KCl

Which of the following lists the samples in order of increasing number of moles in the sample?

• NaCl<KCl<KBr

• NaCl<KBr<KCl

• KCl<NaCl<KBr

• KBr<KCl<NaCl

Which of the following elements has the mass spectrum represented above?

• Mo

• U

• Nb

• Tc

The mass spectrum of a sample of a pure element is shown above. Based on the data, the peak at 26amu

represents an isotope of which of the following elements?

• Al with 13 neutrons

• Mg with 14 neutrons

• Fe with 26 neutrons

• Ti with 26 neutrons

The mass spectrum of the element Sb

is most likely represented by which of the following?

• 
• 
• 
• 

The mass spectrum of element X is presented in the diagram above. Based on the spectrum, which of the following can be concluded about element X?

• X is a transition metal, and each peak represents an oxidation state of the metal.

• X contains five electron sublevels.

• The atomic mass of X is 90.

• The atomic mass of X is between 90 and 92.

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?

• An exothermic chemical change occurred because heat flowed from the contents of the beaker to the room.

• An exothermic physical change occurred because heat flowed from the contents of the beaker and the water on the board to the room.

• An endothermic physical change occurred because the freezing of water is an endothermic process.

• 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.

A 1.0mol sample of He(g) at 25°C is mixed with a 1.0mol sample of Xe(g) at 50°C. Which of the following correctly predicts the changes in average kinetic energy and the average speed of the Xe(g) atoms that will occur as the mixture approaches thermal equilibrium?

• Average Kinetic Energy of Xe Atoms will increase

  
  

  Average Speed of Xe Atoms Will increase

• Average Kinetic Energy of Xe Atoms will increase

  
  

  Average Speed of Xe Atoms Will decrease

• Average Kinetic Energy of Xe Atoms will decrease

  
  

  Average Speed of Xe Atoms Will decrease

• Average Kinetic Energy of Xe Atoms will decrease

  
  

  Average Speed of Xe Atoms Will increase

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?

• The metal temperature changed more than the water temperature did; therefore the metal lost more thermal energy than the water gained.

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

• The metal temperature changed more than the water temperature did; therefore the heat capacity of the metal must be greater than the heat capacity of the water.

• The final temperature is less than the average starting temperature of the metal and the water; therefore the total energy of the metal and water decreased.

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

?

• Water on the blossoms will not freeze unless the air temperature falls significantly below −5°C

• Water is a good thermal conductor that transfers heat from the cold air to the blossoms, keeping the blossoms from going below −2°C

  .

• The freezing of water is an endothermic process; thus, water that freezes on the blossoms absorbs heat from the atmosphere, which in turn keeps the blossoms above 0°C

  .

• 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

  .

The following questions relate to the graph below. The graph shows the temperature of a pure substance as it is heated at a constant rate in an open vessel at 1.0 atm pressure. The substance changes from the solid to the liquid to the gas phase.

• t1

• t2

• t3

• t4

• t5