Evaporation
Objective
Big Idea
Engage
Teacher Tip: This lesson requires internet access and a projector to show the video demonstrations to the class. The videos are taken from the American Chemical Society's website and are a wonderful resource for matter or other chemistry lessons. The students will be working to identify the changes that occur in matter when heat is added to the substance. This works to address NGSS MS-PS1-4.
To start the lesson, students are faced with an independent quick-write question that they will answer in their student notes sheet:
Explain what happens to a rain puddle after it stops raining and the sun comes out.
This prompt is more than likely something they've experienced, and if not, they can at least imagine where the water might go, having experiences rain and/or puddles in the past. After 3-4 minutes, I will ask 2-3 students to share their responses with the class.
Explore
Next, the students will put their heads together to contemplate the next prompt:
How is it that the sun can change a liquid into a gas? Discuss with your peers and write your possible explanation below.
Students should discuss for 2-3 minutes and then write individual responses in their notes sheets once their ideas have been finalized. If they are having a hard time agreeing on an explanation, you can encourage them by asking questions to one or the other (depending on which student is correct) or have them write their own explanation and be prepared to defend it in front of the class.
Explain
For this section you will need internet access and a projector of sorts. I start by previewing the questions in the notes sheet by reading them aloud to the class. I play the demo one time. I play the demo a second time while kids respond to the following:
Watch the demo and explain the following.
-
What happens to the motion of the molecules when we heat liquid molecules?
- What process happens when the molecules get too hot?
The students should be noticing that as heat increases, the energy or motion of the molecules does, as well, thus changing the liquids into gases.
Elaborate
This next section involves the internet, as well, displaying a video demo that asks students to make predictions about hot or cold water and how quickly it will evaporate. I preview the questions by reading them aloud to the class, show the demo, show the demo a second time and give the students a few minutes to respond in their notes sheet:
Watch the following video and make predictions and inferences about what you see.
Prediction: Which bag will evaporate the water faster? Why?
Inference: Which bag evaporated faster? Why?
Evaluate
As a final task, students will individually reflect on the process of evaporation by answering the following prompt:
Explain evaporation in your own words, describing the motion of the molecules within your description.
They should be able to discuss the motion of the molecules getting faster and more spread out to the point where a liquid will change into a gas.
