Question

1) Use the Energy-Interaction Model to explain whether the following statement is true or false: "A quantity of ice at 0℃ must contain less total energy than the same quantity of water at 0℃.

2) According to the definition of heat in the online reading, can an energy system contain a certain amount of heat? Explain.

3) Imagine that you place a piece of copper with an initial temperature of 20℃ in contact with some liquid water with an initial temperature of 100℃. Assume that the physical system consisting of the copper and the water is thermally isolated from everything else; i.e., they can only exchange energy with each other.

a) Sketch two three-phase diagrams, one for each substance, and mark the initial state for each one. Explain in a sentence or two how you can tell if either substance will undergo a phase change during the process of coming to thermal equilibrium. You do not need to do any calculations.

b) Construct a complete energy-system diagram for the process that ends when the two substances are in thermal equilibrium. Don't forget that a complete diagram always includes an algebraic expression of energy conservation.

For parts (c) of this FNT use the same initial conditions for the copper, but assume that the H₂ O is initially in the gas phase at 100℃.

c) Sketch two three-phase diagrams, one for each substance, and mark the initial state for each one. How can you determine if the H₂ O will undergo a temperature change? What calculations and comparisons would you need to make? (Don't actually do the calculations; just explain what you would need to do.)

4) Substance A and substance B initially at different temperatures are placed in thermal contact with each other in a thermally insulated container. Assuming no phase change occurs, explain whether the following statement is true or false:

'The energy that is transferred to or from the object with the larger heat capacity must be greater than the energy that is transferred to or from the object with the smaller heat capacity."

5) A 3.50 kg piece of lead and a 1.5 kg piece of aluminum are placed in contact. They are able to exchange energy as heat, and they can only exchange it with each other. The initial temperature of the lead is 48℃, and the initial temperature of the aluminum is 35℃.

a) If it is possible, construct a single, closed energy-system diagram for the process of lead and aluminum coming to thermal equilibrium. Write an algebraic expression of energy conservation in terms of the △ E s of the two energy systems, and then substitute in the appropriate expressions for the ages. Finally, substitute in all known numerical values. Do you have enough information to find the equilibrium temperature?

b) At an intermediate point in the entire process described above the lead has reached a temperature of 43℃. Follow the instructions for part (a) for the interval that ends when the lead is at a temperature of 43℃. Determine the unknown(s) in your equation.

6) Suppose you used a hot pot to convert a 150 g piece of ice that was initially at -15℃ into liquid water at 50℃.

a) Represent this process in one complete energy-system diagram covering the entire interval.

b) How much heat is added to complete this entire process?

c) If your hot pot has a power rating of 600 watts, show how to find how long it will take to complete the process. (Make sure you are comfortable using standard units of energy, and that you understand the relation of power to energy. Hint: what are Watts?)

Answer 1