Photo Credit: Korte
To help students understand that particle movement changes as a substance changes from one phase to another phase.
This lesson is designed to give students the opportunity to observe a phenomenon created by particle movement.
Prior to this lesson, students should have been introduced to the notion that matter may go through different phase changes. They should be familiar with solids, liquids, and gases. They should also understand that temperature plays an important role in what state a particular type of matter is found. They should understand that heating and cooling a system can impact the phase of that matter. This lesson helps students begin to move from the fundamental concept of solid, liquid, and gas to the reasoning for why the states exist under given conditions.
This particular benchmark may be difficult for students to grasp because middle-school and high-school students are deeply committed to a theory of continuous matter. Students also do not recognize particles as building blocks, but instead believe that they are continuous substances.(Benchmarks for Science Literacy, p. 336.)
Additionally, many students do not understand that all substances undergo some type of movement. Because of this, students have difficulty in appreciating the intrinsic motion of particles in solids, liquids, and gases, and have problems in conceptualizing forces between particles. (Benchmarks for Science Literacy, p. 337.)
Emphasis needs to be placed on helping students understand that there are different motions exhibited by substances in their respective phases. As temperature increases, particle movement increases. When the temperature reaches a certain level, the substance is able to change phase and become a liquid. When this continues, the substance will once again change phase and become a gas or vapor.
Ask students to write descriptions of the three common states of matter. After writing these descriptions, have students go to States of Matter and compare their descriptions to those of solids, liquids, and gases featured on the site. Ask them to record important information they missed about the three states of matter
Explain to students that today they will look at water as it changes from a vapor/gas to a liquid. Briefly outline the experimental procedure with the students. Have the students write a hypothesis as to what they think will happen to particle motion of the water as it changes from a vapor/gas to a liquid: Will particle movement increase, decrease, or stay the same?
Break the class into lab groups of four to five students. Have the students heat water in the open containers to boiling. (Each group of students should heat 200 mL of water.)
Note: This may be done by the teacher as a demonstration.
As the water is heating, ask students:
- What is happening to the water?
- What is heat?
- Why does it matter that the water is heated?
- As the water heats, what is happening to the water particles?
- What is happening between the particles?
After the water has heated to boiling, students should carefully pour the water (200 mL) into the plastic milk container and tightly cap the top. They should observe what happens to the container for a 20 minute time period.
Note: The milk container will almost immediately begin to expand because of the increased particle movement of the water vapor.
As the students are making observations, ask:
- What is happening to the milk container?
- Why is this happening?
- What is making the container do this?
- How could we test this idea?
As the water begins to cool and the milk container goes through another change, ask students:
- Now what is happening to the milk container?
- Why is this happening?
- What is the difference between the water at this time versus the water when we initially poured it into the container?
- What change is happening to the water to make this event occur?
Note: As the water begins to cool and particle movement decreases, the milk container will begin and continue to collapse until it is actually concave.
Students should write a brief explanation of what they observed in the lab. They should work in small groups so they are able to discuss, defend, and clarify their conclusions. They should revisit the hypothesis they wrote prior to the lab.
Have students answer these questions:
- Were there differences between your hypothesis and your conclusion? What were they?
- How has your thinking changed?
- What would happen if you were to reheat the water inside the milk container?
- Would your observations change if you had cooled the water by setting the milk container inside an ice bath?
One way to reinforce this concept is to give each student a balloon and a length of string and tell them:
Tonight you should take this home and blow up and tie off the balloon. Carefully tie the string so that it is tight around the outside of the balloon. Put the balloon and string inside of the freezer for 30 minutes. After that time, check the balloon and record you observations. Check the balloon after an hour and record your observations. We will start by writing our predictions as to what will happen to the balloon over time.
The following class meeting ask students:
- What happened to the balloon?
- How did the size change?
- In what way might particle movement have changed for this to have been observed?
- Would collisions between particles have increased, decreased, or stayed the same?
- Would the overall movement of the particles have increased, decreased, or stayed the same?
- What might happen if we heated the balloon instead of cooling it?
- Is there a way to test this?