1.6, 1.7 Devises Affecting Phase Change

1.6 Conservation of Matter (8.1.6)

Explore this Phenomenon

1. What observation can you make about what you already know is happening in this photo?
2. What questions can you ask?
3. Explain what is happening to the atoms in the paper?

 

8.1.6 Conservation of Mass

Develop a model to describe how the total number of atoms does not change in a chemical reaction, indicating that matter is conserved. Emphasize demonstrations of an understanding of the law of conservation of matter. Balancing equations and stoichiometry will be learned at the high school level. (PS1.B)

In this section, focus on matter. Observe how matter is conserved; the total number of atoms does not change in a chemical reaction.

 

Have you ever lost a screw ?

The following situation happens all too often. You take apart a piece of equipment. When you put the equipment back together, somehow you have an extra screw or two. Or you find that a screw is missing that was there when you started. In either case, you know something went wrong. You should end up with the same amount of material that you started with, not with more or less than what you had originally. This is similar to the idea of conservation of mass.

 

Conservation of Mass

If you build a campfire you start with a large stack of sticks and logs. As the fire burns, the stack slowly shrinks. By the end of the evening all that is left is a small pile of ashes. What happened to the matter you started with? Was it destroyed by the flames? It may seem that way, but in fact the same amount of matter still exists. The wood changed not only to ashes but also to carbon dioxide, water vapor, and other gases. The gases floated off into the air, leaving behind just the ashes.

Assume you measured the mass of the wood before you burned it. Assume you also trapped the gases released by the burning wood and measured their mass and the mass of the ashes. What would you find? The ashes and gases combined would have the same mass as the wood and oxygen you started with.

This example illustrates the law of conservation of mass. The law states that matter cannot be created or destroyed. If matter cannot be created or destroyed, then the matter can only change in some way. Even when matter goes through a reaction, the total amount of matter always remains the same. The total mass of the products must be equal to the total mass of the reactants. In other words, mass cannot be created or destroyed during a chemical reaction.

 

Putting It Together

1. Explain how your understanding of conservation of mass has changed.
2. Think of another phenomenon that applies to the concept of conservation of mass.
3. Explain what is going in the picture based on what you have learned in this section.

 

 

1.7 Devices Affecting Phase Change (8.1.7)

Explore this Problem

Pretend that you want to build a cabin in Utah’s Uinta Mountains. The cabin will get very hot in the summer and very, very cold in the winter. Propose some ideas that will prevent the water in the pipes in your cabin from boiling and freezing.

1. What do you already know that would help in this situation?
2. What do you already know about phase changes in water?
3. What questions can you ask to help explore the situation?
4. How would you go about meeting the challenge?

 

8.1.7: Designing a Device to Affect Phase Change

Design, construct, and test a device that can affect the rate of a phase change. Compare and identify the best characteristics of competing devices, based on data analysis , and modify them to improve the device to better meet the criteria for success. (PS1.B, PS3.A, ETS1.A, ETS1.B, ETS1.C).

In this section, focus on energy and matter. Track the transfer of energy as it flows through matter and affects the rate of a phase change.

 

Changing the rate of a phase change

Phase change occurs when matter changes state. For example when water changes from a liquid to a solid, we say its phase has changed. Phase change is a result of a change in energy. One way to affect the rate of a phase change is to change the amount of energy involved. Increasing the amount of energy will increase the rate of phase change and reducing the amount of energy decreases the rate of phase change. Adding heat is a way to increase the energy involved. Using insulation is a way to reduce heat exchange.

Chemicals can also be used to influence the rate of phase change. For example, antifreeze is an additive that lowers the freezing point of a water-based liquid and raises its boiling point.

 

What is involved in Engineering Design?

Engineering is a creative process where each new version of a design is tested and then modified, based on what has been learned up to that point. This process includes a number of stems:

1. Identifying the problem and defining criteria and constraints.
2. Generating ideas for how to solve the problem. Engineers can use research, brainstorming and collaboration with others to come up with ideas for solutions and designs.
3. Build and then test the prototypes. Using data collected, the engineer can analyze how well the various prototypes meet the given criteria and constraints.
4. Evaluate what is needed to improve the leading design or devise a better one.

To design a solution to the problem, you will need to start by identifying the criteria and constraints. Then develop several possible solutions. Once you have several possible solutions, use the criteria and constraints to evaluate each. You should test the solution that will best meet the criteria and constraints, and then determine how to improve the solution, based on test results. Testing the solution may include modeling, working with materials, using mathematical relationships, etc.

 

In the Science with Engineering Education (SEEd) Standards, specific engineering standards generally involve two types of tasks:

1. If the standard includes the idea of designing, then the design process will components of defining the problem (along with identifying the criteria and constraints), developing many possible solutions, and optimizing a solution (e.g., determining a best solution for the situation based on the criteria and constraints, testing the solution, refining the solution).
2. If the standard includes the idea of evaluating, then the design process will contain components of defining the problem (along with identifying the criteria and constraints) and optimizing a solution. The idea of developing many possible solutions is not included because various solutions will be provided. The idea of evaluating then means determining a best solution from the provided solutions for the situation based on meeting the criteria and constraints requirements.

Which type of engineering task is utilized in this SEEd Standard?

 

Frozen Pipes

Consider the problem of developing something to prevent your pipes from freezing. Many questions would have to be researched in the design process. For example, what is the best type of insulators, what temperature does water boil and freeze at, what insulators are cheap and easy to work with? What are the constraints on the project? Is there a budget limit? Does it have a maximum size or weight that the pipes can hold?

After researching the answers, possible designs are developed. This generally takes imagination as well as reasoning based on what you found out during research. Then a model must be designed and tested. This allows any problems with the design to be worked out before a final design is selected and produced.

After testing your model, you will probably need to modify it and retest it until you reach a design that satisfies the need and fits within the constraints. At this point you would share the device you have created with others for production or as a solution to the problem.

In order to engineer a solution to our problem with the pipes in the cabin you should know the difference between thermal conductors and thermal insulators. The following information will give you a brief breakdown of information that could be useful to you.

 

Movement of Heat Energy

• Conduction: heat is transferred from one object to another by direct contact
• Convection: heat is moved by particles moving in a fluid (gas/liquid)
• Radiation: heat flows through empty space (no physical contact--just waves of energy)

 

Changing the rate of phase change (change of state)

• One way to affect the rate of phase change is to change how much heat is involved
  • Add more heat = faster melting or evaporation
  • Remove more heat = faster freezing or condensation

 

• A second way to affect the rate is by adding chemicals
  
  • adding chemicals can change the boiling point or freezing point of the mixture
  • so it takes greater addition/removal of energy to change state
  • Examples: 
    • Adding antifreeze reduces the freezing point, so temperatures have to get much colder to freeze
    • Adding salt to boiling water increases the boiling point, so it takes hotter temperatures to change the liquid to gas

 

Thermal Conductors

Conduction is the transfer of thermal energy between particles of matter that are touching. Thermal conduction occurs when particles of warmer matter bump into particles of cooler matter and transfer some of their thermal energy to the cooler particles. Conduction is usually faster in certain solids and liquids than in gases. Materials that are good conductors of thermal energy are called thermal conductors. Metals are especially good thermal conductors because they have freely moving electrons that can transfer thermal energy quickly and easily.

• Third way to change rate of phase change is to change how well the heat can move
  • Thermal Conductors: Materials that are good at conducting (transferring) heat energy
    • Metals have freely moving electrons, and make great conductors
    • Stone

 

Thermal Insulators

One way to retain your own thermal energy on a cold day is to wear clothes that trap air. That’s because air, like other gases, is a poor conductor of thermal energy. The particles of gases are relatively far apart, so they don’t bump into each other or into other things as often as the more closely spaced particles of liquids or solids. Therefore, particles of gases have fewer opportunities to transfer thermal energy. Materials that are poor thermal conductors are called thermal insulators. Down-filled snowsuits, like those in the next image, are good thermal insulators because their feather filling traps a lot of air.

Fine soft feathers like these fill the snowsuits on the left.  The feathers keep birds as well as people warm!

Another example of a thermal insulator is pictured in the next picture. The picture shows fluffy pink insulation inside the attic of a home. Like the down filling in a snowsuit, the insulation traps a lot of air. The insulation helps to prevent the transfer of thermal energy into the house on hot days and out of the house on cold days. Other materials that are thermal insulators include plastic and wood. That’s why pot handles and cooking utensils are often made of these materials. Notice that the outside of a toaster is made of plastic. The plastic casing helps prevent the transfer of thermal energy from the heating element inside to the outer surface of the toaster where it could cause burns.

• • Thermal Insulator: Material that is not good at conducting heat energy
    • Plastics
    • Foam
    • Gas 
    • Wood
    • Tin foil

 

Putting It Together

1. Explain how your ideas of how you could redesign this cabin have changed.
2. Think of another phenomenon that applies transfer of heat.
3. Explain what causes insulation to be necessary based on what you have learned in this section.