Lesson 7. Lesson 7 - Modeling State Changes

Umit Aslan, Umit Aslan, Royi Lachmy, Umit Aslan
Chemistry
N/A
Introductory High School Chemistry
v1

Overview

Will be updated soon.

Standards

Computational Thinking in STEM
  • Computational Problem Solving Practices
    • Developing Modular Computational Solutions

Acknowledgement

Cite the Modelsim research

Activities

  • 1. Purpose and Brainstorm
  • 2. Exploration 1 - Predict
  • 3. Exploration 1 - Observe
  • 4. Exploration 2 - Model
  • 5. Exploration 2 - Predict
  • 6. Exploration 3 - Predict
  • 7. Exploration 3- Experiment
  • 8. Follow-up
  • 9. Exploration 3 - Making sense of your model

Student Directions and Resources


You should now be feeling more comfortable with how particles interact with one another. In particular, we've spent a lot of time experimenting with how particles in a gaseous state interact and how properties such as pressure and temperature emerge from those interactions. You've also been introduced to a model that shows how particles in a liquid state act differently than those same particles in a gaseous state. In this activity, we'll begin to theorize about how particles might shift between the liquid and gas state.

1. Purpose and Brainstorm


Consider how you might model evaporation and boiling?

Read the brainstorm topic below, then write your response in the blank box.


Question 1.1

How might you model evaporation and boiling? Consider what is happening to the molecules of a liquid when it is boiling and what type of observations would you want to make in order to give you evidence that a liquid was boiling?

2. Exploration 1 - Predict


Question: What causes boiling?

Predict: Watch the video below that shows an interesting phenomenon. Use your observations to answer the following questions.


Question 2.1

Is this an open or closed system?



Question 2.2

Before experiment, observe the liquid in the flask. Is it boiling?



Question 2.3

How can you tell?



Question 2.4

If the experimenter did not heat or cool the liquid any more, but simply pushed or pulled on the syringe, would that alone be enough to cause the liquid to start boiling? Why?

3. Exploration 1 - Observe


Watch the liquid closely as the experimenter pushes and pulls on the syringe. Answer the following questions.


Question 3.1

What do you observe is happening in the liquid?



Question 3.2

If someone claimed that pulling on the syringe is changing the boiling point of the liquid, what evidence would support that claim?

4. Exploration 2 - Model


Question: How can we model boiling?

Model

As a group model to explain why changing the pressure of the air above the liquid might be changing whether the liquid boils or not.

  1. As a class do this together: Label a piece of paper as “Syringe before”. Discuss how to use pennies and oyster crackers to represent air molecules and water molecules. Include a key to represent the type of molecules and the speed of the molecules.
  2. Discuss as a class:  Should there be any water molecules in the air above the syringe? Is is possible some water has evaporated already?
  3. As a group, make your own copy of the class consensus model for the “Syringe before” on a single piece of paper.
  4. As a group, now label a new piece of paper as “Syringe after pulling”. Using the same number of pennies and oyster crackers, make a 2nd physical model showing the state of syringe when the plunger is pulled out and bubbles of water are forming and raising to the top of the liquid.
  5. Discuss as a group:  Should there be the same number of water molecules in the air above the syringe as before?

5. Exploration 2 - Predict



Question 5.1

Based on the models you made, sketch the predicted shape of the graph of the pressure of the air in the syringe as the plunger is pulled upward over time.

Note: Draw your sketch in the sketchpad below


Question 5.2

Based on your models, sketch the predicted shape of the graph of the concentration of water molecules in the air as the syringe is pulled upward over time.

Note: Draw your sketch in the sketchpad below


Question 5.3

If the syringe could be compressed to half the volume as the syringe before, would that affect concentration of water molecules in the air above the syringe?

  A lower concentration of water molecules would be in the air than were in the air before.
  The same concentration of water molecules would be in the air as before
  A higher concentration of water molecules would be in the air than before


6. Exploration 3 - Predict


Question: How can we model evaporation?


Question 6.1

1.  Will water evaporate as fast in a closed system as in an open system?



Question 6.2

2.  Why?

7. Exploration 3- Experiment


Consider the following experiment and its results. Then answer the questions below.

  1. A group conducts an experiment to test the rate of evaporation in a closed vs, and open system. They gather the following supplies:
    • a cup with a small bit of rubbing alcohol in it
    • a petri dish
    • two eyedroppers
    • a clock
  2. They fill two eyedroppers with rubbing alcohol and place two drops of alcohol on the table at the same time. They start the timer and immediately, cover one with a glass dish (see the photograph on the right)
  3. They check every 1 hour to see if either drop has evaporated completely. At 2 hours, drop B in the open system has evaporated completely, but drop A in the closed system has not.
  4. They continue for observing, now every hour, and at the end of the day (8 hours later), drop A still hasn't evaporated completely.
Substance & Condition Time to evaporate completely
Drop A: 1 drop of rubbing alcohol in a closed system       Unknown if it will happen at all, but if it does happen at some point it will take over 8 hours.
Drop B: 1 drop of rubbing alcohol in an open system        About 2 hours.

Question 7.1

At 10 seconds after the experiment for each of the two conditions: Draw a model of the initial drop of liquid in a closed system after 1 hour.



Question 7.2

At 10 seconds after the experiment for each of the two conditions: Draw a model of the initial drop of liquid in an open system after 1 hour.



Question 7.3

Step 1 – You are going to create a molecular model of the drop of liquid evaporating.  A drop of alcohol has millions of billions of alcohol molecules in it.  This is too many for you to draw in a model.  So pick a reasonable number of molecules to represent in a drop of alcohol that you can draw quickly.

Step 2 - Draw a model to show the molecules of alcohol in a drop of alcohol. Include the same key as before, using circles to represent one type of molecule and hexagons to represent another type. 

Note: Draw your sketch in the sketchpad below


8. Follow-up



Question 8.1

How is evaporation similar to boiling?



Question 8.2

How is it different?



Question 8.3

How do the behaviors of evaporation and boiling both depend on the presence of gravitational force and on intermolecular attaction-repulsion forces?

9. Exploration 3 - Making sense of your model



Question 9.1

How does your model help explain why the drop in the open system evaporates more quickly than the one in the closed system?



Question 9.2

Your teacher will assign your group one of these factors. Check the box next to the factor you are assigned below:

  The amount of surface area of liquid exposed to the air
  The temperature of the liquid
  The temperature of the air above the liquid
  The wind speed of the air above the liquid
  The air pressure above the liquid
  The amount of humidity in the air above the liquid


Question 9.3

Why would changes to that factor probably affect the rate of evaporation?