AP Chem Unit 6.3: Heat Transfer and Thermal Equilibrium

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?

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.

A student adds 50.0g50.0g of liquid water at 25.0°C25.0°C to an insulated container fitted with a temperature probe. The student then adds 10.0g10.0g of ice at 0.0°C0.0°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?

Once all of the H2OH2O molecules are in the liquid phase, the individual molecular speeds either increase or decrease until all the particles have the same speed.

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, but the metal lost the same amount of thermal energy as the water gained.