Rework referenced MW model for visual simplicity. Only variable needed is total energy, and it can be conveyed with color.

Engage/Elicit:

How do you think water changes states?

Ed: Is "change state" too advanced an expression for 5-6? 
Matt: We took that expression from the CA texts & stds.

L5 Write your response in the text box below. L4 How do you think ice changes to water? How do you think water changes to ice? L3 Ice can change to water when ____. Water can change back to ice when _____ L2 What is most important in changing ice to water? (Adding heat energy, taking heat energy away) L1 In order for ice to melt you need to add energy. Use the text box below to explain your answer.

Explore:

The model below describes water in its solid form (ice).

MW model from ITSI: Activity 58: Latent Heat http://itsi-portal.concord.org/diy/view/58/

Part I: Heating

1. Click "Take snapshot." A window will pop up with a picture of your model. In the text box, replace "Add a note describing this image..." with your own description of your picture. This is water in its solid state, or ice.
2. Investigate adding heat to the system. Add energy to the system by clicking on the "Start adding heat" button below the model window.
3. Try to watch the water as it melts. When you think you see liquid water, pause the simulation by clicking the button with the two vertical lines: Cannot resolve external resource into attachment.
4. If you need to try again, click the back button on the model: Cannot resolve external resource into attachment.
5. Click "Take snapshot." A window will pop up with your picture. In the text box, replace "Add a note describing this image..." with your own description of your picture.

   L5 Describe your picture in the text box. L4 Make sure you include the name of the state and a description of the structure of the molecules. L3 The water's state is _____. The molecules are ______ L2 Is it solid, liquid or gas? What are the molecules doing? L1 The water is in its liquid state, and the molecules are moving around. Explain in the text box.

6. The process you observed is called melting. What changes occurred and what did you do to cause them?

   L5 Write your answer in the text box below. L4 Describe the changes that occurred to the molecules. What was added to the system to cause the change? L3 As the water melted, the molecules started ______ because we added _______. L2 As the water melted, the molecules started moving because (we added heat energy, the "stickiness" of the bonds wore off, the ice fell apart) L1 The heat energy we added made the water melt. Describe this below.

7. Now continue running the simulation of adding heat by clicking the play button: Cannot resolve external resource into attachment.
8. When all the water evaporates into gas, click the pause button: Cannot resolve external resource into attachment.
9. Click "Take snapshot." A window will pop up with your picture. In the text box, replace "Add a note describing this image..." with your own description of your picture.

   L5 Describe your picture in the text box. L4 Make sure you include the name of the state and a description of the structure of the molecules. L3 The water's state is _____. The molecules are ______ L2 Is it solid, liquid or gas? What are the molecules doing? L1 The water is in its gaseous state, and the molecules are moving around freely, without being bonded to each other. Explain in the text box.

10. The process you observed is called evaporation. What changes occurred and what did you do to cause them? How did the bonds between the molecules change?

    L5 Write your answer in the text box below. L4 Describe the changes that occurred to the molecules. What was added to the system to cause the change? L3 As the water melted, the molecules started ______ because we added _____. The bonds between the molecules ______. L2 As the water melted, the molecules were freed from their bonds because (we added heat energy, the "stickiness" of the bonds wore off, the water fell apart). L1 The heat energy we added made the water evaporate. Describe this below.

    Part II - Cooling

In the second model below, we will investigate removing heat energy from the system.

MW model starting with a gas of atoms

1. Start the simulation by clicking the triangular "start cooling" button.
2. Observe the changes of state as heat energy is taken out of the system.
3. What phase changes do you observe? Describe what you see.

   L5 Describe you answer in the text box below. L4 What happens to the molecules as the heat energy is removed? L3 As the heat energy is removed, the molecules ___. I see the ___ phase, then the ___ phase and finally the ____ phase. L2 The molecules get closer together and form the (gas, liquid, solid phase). Eventually they form a regular shape that does not change, in the (gas, liquid, solid phase). L1 The molecules get closer together in the liquid phase, and then they get "locked" together in the solid phase.

Explain:

Heating

The key to change of state is the change in the energy in the system. As you saw in the model, heating water up, or adding heat energy made it change state.

First, you observed water change from solid to liquid (ice to liquid water). The solid water has a regular pattern, with molecules bound tightly together. The solid water does not change shape, and has the lowest total energy:
Cannot resolve external resource into attachment.

As the heat energy was added and the total energy of the water increased, eventually the molecules started to move around and the object changed shape. The change of state from solid to liquid is what we call melting it takes energy to melt water, which is why we added heat energy:
Cannot resolve external resource into attachment.

Finally, molecules start to escape the bonds with the other molecules, and move freely. This is the gaseous state. When water changes from liquid to gas, it's called evaporation. It takes energy to evaporate water, which is why we keep adding heat energy.
Cannot resolve external resource into attachment.

Cooling

What happens in cooling is the exact reverse of the heating process. Instead of taking in more heat energy, the water molecules are giving off heat energy. When a gas loses energy, it moves back into the compact liquid form in a process called condensation:
Cannot resolve external resource into attachment.
You can see that the total energy in the liquid form is lower than that in the gas form. This water has given off heat energy as it condensed.

Finally, the liquid water can be turned back into ice, or solid water. This process is called freezing. You have to take a lot of heat energy away to freeze water; a freezer works pretty hard to pump the heat energy away, allowing water to freeze:
Cannot resolve external resource into attachment.
You can see that the solid has the least total energy, just as it began. In fact, it takes the same amount of energy to heat the water through these changes of state as is released by the water when it returns from gas to liquid to solid, its original state!

Button_Play.png (image/png)
Button_Pause.png (image/png)
Button_Back.png (image/png)
Snapshot_Solid.png (image/png)
Snapshot_Liquid.png (image/png)
Snapshot_Gas.png (image/png)

Ed: this activity is too long.  Could this activity be broken into two parts? a) melting and evaporating, b)condensing and freezing OR: a) melting and freezing (solid - liquid only), b) evaporating and condensing (liquid - gas only) Posted by ehazzard at Aug 09, 2007 11:14

It's an idea. Would we nix another activity? UDL Water\-Activity 4\-Why does it rain more near the coast than inland\? \(5\-6\) is anemic. Posted by mateoaw at Aug 11, 2007 14:52