Thermal Energy Review

Ms. Byrd cooked a pot of soup, then put half the soup in the freezer for a while. Now the soup in the pot is hot, and the soup in the freezer is cold. What is the difference between the molecules of the soup in the pot and the molecules of the soup in the freezer?

• The molecules of the soup in the pot are moving and the molecules of the soup in the freezer are not moving.

• The molecules of the soup in the pot are moving faster than the molecules of the soup in the freezer.

• There is no difference because all of the soup is made of the same type of molecules.

• The molecules of the soup in the freezer are smaller than the molecules of the soup in the pot.

Mr. Griff is stacking chairs on top of another chair after the boys basketball game. Both chairs are the same size and have the same number of molecules. The diagram below shows the chairs before they touch. Use the information in the diagram to answer the question. How does the temperature of the bottom chair compare with the temperature of the top chair before the chairs touch? What will happen after the chairs have been touching for a while?

• Before the chairs touch, the bottom chair is cooler than the top chair. Once the chairs are touching, the top chair will transfer kinetic energy to the molecules in the cooler bottom chair until both chairs reach the same temperature, which will be in between their starting temperatures.

• Before the chairs touch, the bottom chair is hotter than the top chair. Once the chairs are touching, the bottom chair will transfer kinetic energy to the molecules in the cooler top chair until both chairs reach the same temperature, which will be in between their starting temperatures.

• Before the chairs touch, the chairs are at different temperatures. Once the chairs are touching, both kinetic energy and cold energy will transfer between the molecules in the two chairs until both chairs reach the same temperature, which will be in between their starting temperatures.

• Before the chairs touch, the bottom chair is hotter than the top chair. Once the chairs are touching, the cooler top chair will gain kinetic energy until the molecules in both chairs have an energy of 35, because hotter things increase the temperature of cooler things.

Michael puts a hockey puck onto ice. After a while the temperature of the hockey puck decreases. What happens to the molecules of the hockey puck when the temperature of the puck decreases?

• The hockey puck loses heat molecules.

• The energy of the molecules in the hockey puck increases.

• The energy of the molecules in the hockey puck decreases

• The cold energy of the molecules in the hockey puck increases.

After the laptops have been touching for a while, will Sam’s laptop or Odessa’s laptop be cooler, and why?

• Sam’s laptop will be cooler than Odessa’s laptop, because less energy has to transfer for the molecules of Sam’s laptop to reach the same temperature as the molecules of Arun’s laptop.

• Both laptops will be the same temperature, because both Arun’s and Mari’s laptops had the same amount of energy to transfer and the molecules in Sam’s and Odessa’s laptops started with the same energy.

• Odessa’s laptop will be cooler than Sam’s laptop, because Odessa’s started with more total energy, so less energy has to transfer for her and Arun’s laptops to reach the same total energy.

• Odessa’s laptop will be cooler than Sam’s laptop, because the energy that transferred to Odessa’s was spread out over more molecules.

Answer explanation

Mari and Sam's laptops are the same sizes vs Arun and Odessa's laptops; where Odessa's laptop is larger than Arun's. Because of this, Mari's and Sam's laptop will reach equilibrium quicker than Arun and Odessa's. An equal amount of kinetic energy will transfer from Mari's to Sam's. In Arun's and Odessa's, Arun's laptop will have to transfer MORE kinetic energy to Odessa's because more molecules are needed to reach equilibrium.

Describe why the molecules in an ice pack get warmer overtime when you leave it on your arm. Be sure to describe how kinetic energy transfers and how speed of the molecules changes.

• Because kinetic energy transfers from your arm to the ice pack, causing the molecules in the ice pack to move faster and get warmer over time.

• Because the ice pack generates its own heat, making the molecules move slower.

• Because the molecules in the ice pack lose energy to your arm, causing them to get colder.

• Because the ice pack absorbs light from the environment, making the molecules move slower.

What will the afternoon diagram look like once the warm water meets the air inside the school?

Create your drawing in the diagram use the keys to help.

In some places, hot water from underground can shoot up into the air through a hole in the ground. When this happens, the ground surrounding the water increases in temperature. What happens to the molecules in the ground when the temperature of the ground increases?

• More heat molecules combine with the molecules in the ground.

• The energy of the molecules in the ground decreases.

• The energy of the molecules in the ground increases.

• The cold energy of the molecules in the ground decreases.

Claude is in the kitchen cooking and is going to stack one pan on top of another pan. The two pans are the same size and have the same number of molecules. Use the information in the diagram to answer the question.

What is true about the two pans before they touch each other?

• Before the pans touch, the bottom pan is hotter than the top pan. Once the pans are touching, the cooler top pan will gain kinetic energy until the molecules in both pans have an energy of 70, because hotter things increase the temperature of cooler things.

• Before the pans touch, the bottom pan is hotter than the top pan. Once the pans are touching, the bottom pan will transfer kinetic energy to the molecules in the cooler top pan until both pans reach the same temperature, which will be in between their starting temperatures.

• Before the pans touch, the two pans are at different temperatures. Once the pans are touching, both kinetic energy and cold energy will transfer between the molecules in the two pans until both pans reach the same temperature, which will be in between their starting temperatures.

• Before the pans touch, the bottom pan is cooler than the top pan. Once the pans are touching, the top pan will transfer kinetic energy to the molecules in the cooler bottom pan until both pans reach the same temperature, which will be in between their starting temperatures.

Answer explanation

The pans are the same size with the same number of molecules. The bottom pan is warmer and therefore will transfer kinetic energy to the top pan when the pans touch. As we know, energy transfers until the temperatures reach equilibrium which will be somewhere in between the two temperatures.