To determine the effect of temperature on the motion of particles.
One of the most important concepts for students to understand is that temperature affects the motion of molecules. As air is warmed, the energy from the heat causes the molecules of air to move faster and farther apart. Some students may have difficulty with this concept because they lack an appreciation of the very small size of particles or may attribute macroscopic properties to particles. Students might also believe that there must be something in the space between particles. Finally, students may 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.336.) In order to clarify student thinking about molecules and their relationship to temperature, instruction has to make the molecular world understandable to students.
The primary purpose of these activities is to introduce the students to the concept that temperature causes molecules and atoms to move faster and farther apart, which in turn causes the change from solid to liquid, and liquid to gas. Students need to come to this activity with the knowledge that some solids turn into liquids when heated. They also need to understand the observable differences between a solid and a liquid.
In "The Balloon and the Bottle," students experience the effects of increased temperature on air inside a balloon. As the air contained inside the balloon begins to warm, the molecules begin to strike the sides of the balloon harder and more often. This increases the air pressure and causes the balloon to expand. This activity also provides an opportunity to reinforce concepts related to the conservation of matter. According to research, many students in 6th and 7th grade still appear to think of weight simply as "felt weight" - something whose weight they can't feel is considered to have no weight at all. Measuring the weight of the bottle, balloon, and water at room temperature, after heating and after cooling, may help students dispel this misconception. If the balloon is not broken, the weight should stay the same. Research also states that many students can understand qualitatively that matter is conserved in transforming from solid to liquid. They also start to understand that matter is quantitatively conserved in transforming from solid or liquid to gas - if the gas is visible.(Benchmarks for Science Literacy, p.336.)
Before you start the activity, students need to understand the difference between particles in a gas, liquid, and a solid. Have students look at the Gases, Liquids, and Solids page on the Purdue University Chemistry Department website. Here they will see how the characteristics of solids, liquids, and gases can be explained by particle motion.
Discuss what happens at both the observable and molecular level in these scenarios:
- Water is placed in the freezer.
- Ice melts.
- A puddle evaporates.
Use the following demonstration to begin a discussion of the effect of temperature on particle movement. Blow up a balloon, and then aim a hair dryer on low setting at the balloon, and watch it rise.
- What happens when I blow hot air on the balloon? Why?
- What is happening to the air inside the balloon?
- What do you think would happen if the balloon was placed in a cold car?
- What would happen to the balloon as the temperature increases in the car? Why?
- Ask the students to think about what might happen to a balloon in a bottle when it is heated.
The Balloon and the Bottle
Give each student a copy of the Balloon and the Bottle student sheet, which includes questions and procedures.
Briefly review the procedure with students:
- Pour about 15 ml. (1 tbsp) of water into an empty glass bottle/flask.
- Weigh the bottle, water, and balloon using the balance. Record the weight on the data table.
- Stretch the open balloon over the top of the bottle.
- Heat the bottle until the water boils vigorously. Write down your observations of the water and the balloon on the data table.
- Using an oven mitt, place the bottle with balloon on the balance. Record the weight on the data table.
- Allow the bottle to cool. Write down observations of the balloon and the bottle.
- Weigh the bottle and the balloon. Record information on the data table.
After students understand the procedure, ask them to make these predictions:
- Will the weight change when the flask/bottle, water, and balloon are heated/cooled?
- What do you think will happen to the balloon when the bottle is heated/cooled?
- What is going to happen to the water when it is heated/cooled?
After students have completed the activity, ask them to record their answers to these questions on the student worksheet:
- Compare your observations to your predictions.
A. Were your predictions correct?
B. Did anything surprise you during the experiment? If so, describe it.
- What do you think caused the balloon to expand? What's going on outside the balloon that's causing this to happen?
- Why do you think the balloon was sucked into the bottle? What's going on outside the balloon that's causing this to happen?
- What did you observe inside the bottle as it cooled?
- What's happening to particles inside the balloon? Are they moving? Were they moving?
- How did this experiment demonstrate water changing from liquid to gas?
- What would have happened if the bottle were placed in the freezer?
In this assessment activity, students will illustrate in a cartoon scene the idea of how temperature affects the motion of molecules. Students should present their cartoon to the class and explain how it relates to the idea of temperature affecting the motion of molecules and states of matter.
Students should be assessed on how well their cartoons convey the following scientific ideas:
- How heating and cooling affects the movement of particles.
- How states of matter may change with heating and cooling.
Give the students these instructions:
You are a cartoonist. Your task is to create a cartoon scenario illustrating the effect of temperature on the movement of molecules in a solid, liquid, or a gas. You will use your cartoon to teach your classmates about the movement of molecules in the different states of matter and how an increase or decrease in temperature affects them.
Go to Full of Hot Air! on the Science for Kids website. This activity allows the students to find out what happens when you heat a gas and cool it down. Have them compare the results of this activity to those of "Balloon in a Bottle."
Students could use the Web to find out other experiments that could be used to illustrate the effect of temperature. They could also find out about real life illustrations of how temperature affects everything. This would be a good opportunity to help students learn how to do a guided Web search at home or in school.
The purpose of this activity is to allow students the opportunity to review new concepts and terminology related to states of matter. This would be a great way for students to review for tests.
- Generate words, phrases, or drawings that come to mind when they think of: States of Matter and Temperature
- Work in small groups to share ideas and group them into categories.
- Observe and analyze the work of other groups. One student stays behind at the table to answer questions and to note which cards are clear to the other students and which ones need further clarification..
- Discuss what they observed and to revise or add new ideas/categories based on class feedback.
- Create a class set of the cards. Students can keep their cards in an index box for further study.