# 3.3: Energy

Difficulty Level: At Grade Created by: CK-12

## Student Behavioral Objectives

The student will:

• explain the difference between kinetic and potential energy.
• state the law of conservation of matter and energy.
• define heat.
• define work.

## Timing, Standards, Activities

Timing and California Standards
Lesson Number of 60 min periods CA Standards
Energy 1 None

### Activities for Lesson 3

Laboratory Activities

1. Energy Lab - Recognizing Potential Energy

Demonstrations

1. None

Worksheets

1. None

1. The Nature of Energy

## Answers for Energy (L3) Review Questions

• Sample answers to these questions are available upon request. Please send an email to teachers-requests@ck12.org to request sample answers.

## Multimedia Resources for Chapter 3

The following web site has a video that defines matter and energy.

You may listen to Tom Lehrer’s humorous song “The Elements” with animation at this website.

This website provides a review about matter and the categories of matter.

This website provides some free PowerPoint presentations. The presentation on “Matter and Energy" provides a review of some properties of matter, as well as provide examples of the topics covered in this lesson.

This website has lessons, worksheets, and quizzes on various high school chemistry topics. Lesson 1-5 is on physical and chemical properties, as well as physical and chemical changes.

Summary of concepts of matter and energy and benchmark review.

## Teacher's Pages for Chemical and Physical Changes

Lab Notes

This lab requires extensive setup. It is best to set up the equipment for the students so they can come in and not waste time. Allow two periods or a double period to complete this lab.

It is best to prepare the copper turnings for the students. To prepare a ball of turnings, cut some of the turnings off of the mass of turnings and place it in the palm of your hand. Roll the turnings between the palms of your hands until the ball becomes small enough to fit wholly within a crucible. When rolling between the palms, do not apply too much pressure. This can cause the sharp edges of the copper turnings to abrade your hands. Do NOT pull the turnings apart with your fingers. The edges of the turnings are sharp enough to cause deep cuts to you fingers and hands if placed under even moderate tension, and these cuts are painful and slow to heal.

The copper(II) nitrate is hygroscopic and is often clumped together. If needed, chip the material apart with a scoopula, and if necessary, break the larger chunks up with a mortar and pestle. Do NOT grind nitrates too vigorously, and do not mix them with an easily oxidizable substance. Store the copper(II) nitrate in an airtight re-sealable container to prevent caking.

The destructive distillation of wood produces methanol vapor, which sometimes ignites. It is a good tip to remind the students to sometimes expect the unexpected. It is a good way to keep them alert and not tip them off to an interesting observation. It may not even occur, but often does. After this experiment, the test tubes are so fouled with tar and other decomposition products that it is actually time effective to discard them. When the students are done heating the tubes have them set it aside to a place where the likelihood of it being touched is low. They stay hot for a long time.

For the \begin{align*}NaCl\end{align*} procedure, use a watch glass. Using a glass slide almost always leads to the slide breaking due to thermal stress.

The destructive distillation of wood produces quite a bit of smoke. Do this lab in a well ventilated room, and inform the administration that this lab is being performed so they do not think that there is a wood fire in the building by the odor.

Solutions to Prepare

Per Lab Group

• \begin{align*}1 \ mL\end{align*} of approximately \begin{align*}0.10 \ M \ NaCl\end{align*} solution \begin{align*}(0.6 \ g/100 \ mL)\end{align*}
• \begin{align*}1 \ mL\end{align*} of approximately \begin{align*}0.10 \ M \ AgNO_3\end{align*} solution \begin{align*}(1.7 \ g/100 \ mL)\end{align*}
• \begin{align*}1 \ mL\end{align*} of approximately \begin{align*}0.10 \ M \ FeCl_3\end{align*} solution \begin{align*}(1.6 \ g/100 \ mL)\end{align*}
• \begin{align*}1 \ mL\end{align*} of approximately \begin{align*}0.10 \ M \ KSCN\end{align*} solution \begin{align*}(1 \ g/100 \ mL)\end{align*}
• \begin{align*}1 \ mL\end{align*} of approximately \begin{align*}0.10 \ M \ HNO_3\end{align*} (dilute \begin{align*}6.25 \ mL\end{align*} conc nitric acid to \begin{align*}1.0 \ liter\end{align*})

## Lab - Chemical and Physical Changes

Background Information

Matter is characterized in different ways using physical and chemical properties. Some physical properties are: color, odor, density, hardness, magnetism, solubility, melting point, and boiling point. Chemical properties are determined by the reaction of a substance with other substances. Examples of chemical properties are the following: reacts with acids, reacts with oxygen in air, decomposes on heating, and is acidic or basic. Chemical and physical properties must not be confused with chemical and physical changes. Physical changes refer to a transformation of a state. The chemical composition of the substance remains the same. Chemical change refers to the production of new substances that may have physical and chemical properties different from the original substance. Chemical changes are occurring when there is a drastic change in color, a gas or light or sound is produced, a mass change occurs, or a solid is formed where there was none before.

In this experiment, you will investigate the difference between chemical and physical changes in matter. You are to perform several short exercises and observe the changes that occur during each. You will then determine if your procedure resulted in chemical or physical changes.

Purpose

The purpose of this activity is to observe and document chemical and physical changes in matter.

Apparatus and Materials

• Binocular microscope
• crucible
• test tube rack
• test tube holder
• forceps
• disposable pipettes
• scoopula
• 2 test tubes \begin{align*}(13 \times 10 \ mm)\end{align*}
• laboratory burner
• 3 test tubes \begin{align*}(18 \times 150 \ mm)\end{align*}
• ring stand and ring
• clay triangle
• watch glass
• wood splint
• matches
• crucible tongs
• solid \begin{align*}NaCl\end{align*}
• solid copper turnings
• solid \begin{align*}Cu(NO_3)_2\end{align*}
• \begin{align*}1 \ mL\end{align*} of approximately \begin{align*}0.10 \ M \ NaCl\end{align*} solution
• \begin{align*}1 \ mL\end{align*} of approximately \begin{align*}0.10 \ M \ AgNO_3\end{align*} solution
• \begin{align*}1 \ mL\end{align*} of approximately \begin{align*}0.10 \ M \ FeCl_3\end{align*} solution
• \begin{align*}1 \ mL\end{align*} of approximately \begin{align*}0.10 \ M \ KSCN\end{align*} solution
• \begin{align*}1 \ mL\end{align*} of approximately \begin{align*}0.10 \ M \ HNO_3\end{align*}
• solid calcium carbide, \begin{align*}Ca_2C\end{align*}
• distilled water

Safety Issues

Hot glassware; handle with forceps or crucible tongs. The solutions used can be corrosive and or poisonous. Heating wood can cause copious fumes. Perform this lab in a well ventilated room

Procedure for Part I

1. Heating a wood splint. Obtain a wood splint and break it into small pieces. Place several pieces in a large test tube. Using a test tube holder, heat the test tube strongly for several minutes. CAUTION: Hot glass. Record your observations in the data table.
2. \begin{align*}NaCl\end{align*} and water. Place a spatula of sodium chloride in a watch glass. Add \begin{align*}3-5 \ mL\end{align*} of water and stir the salt and water to dissolve. Using the crucible tongs, hold the watch glass over a low flame of a Bunsen burner until the water has evaporated. After the watch glass and the solid have cooled, examine the residue with a binocular microscope. Compare the residue to a fresh sample of \begin{align*}NaCl\end{align*}.
3. Heating copper. Clean and dry your crucible. To dry the crucible, heat strongly for \begin{align*}2\end{align*} to \begin{align*}3 \ minutes\end{align*} and let cool. CAUTION: Hot crucibles should be handled only with tongs or forceps. While the crucible is cooling, obtain a small amount of copper turnings from the supply table. If not done already, roll them into a ball about \begin{align*}2 \ cm\end{align*} in diameter and place the ball in the crucible. Measure the mass of the crucible and copper to the nearest \begin{align*}0.01 \ g\end{align*}. Heat the metal in the crucible over a hot flame for five minutes, cool and measure the mass.
4. Heating \begin{align*}Cu(NO_3)_2\end{align*} CAUTION: Proper ventilation must be used. Do not inhale the fumes; avoid skin contact. Using a spatula, obtain a few crystals of copper(II) nitrate, \begin{align*}Cu(NO_3)_2\end{align*}, and place them in a large test tube. Heat slowly over a low flame until a change is observed. Then, heat strongly until the reaction is complete. Let the mixture cool, and then add 10 drops of dilute nitric acid, \begin{align*}HNO_3\end{align*}. Heat gently.
5. Combining solutions. Obtain 3 clean small test tubes and mix the following solutions:
1. To 5 drops of sodium chloride, \begin{align*}NaCl\end{align*}, solution add 5 drops of silver nitrate, \begin{align*}AgNO_3\end{align*}, solution. CAUTION: Silver nitrate can cause burns. Avoid skin contact.
2. To 5 drops of iron (III) chloride, \begin{align*}FeCl_3\end{align*}, solution add 1 to 3 drops of Potassium Thiocyanate, \begin{align*}KSCN\end{align*}, solution. Observe and record your observations.
3. To 5 drops of \begin{align*}FeCl_3\end{align*} solution add 1 to 2 drops of silver nitrate, \begin{align*}AgNO_3\end{align*}, solution. CAUTION: \begin{align*}AgNO_3\end{align*} causes burns, avoid skin contact. Observe and record your observations.
6. Calcium carbide and water. Add \begin{align*}5 \ mL\end{align*} of water to a watch glass, and place a chunk about the size of a pea of calcium carbide into it. Record your observations. Light the emitted gas with a wooden splint or match.
Data and Observations
Experiment Observations Chemical or Physical Change
Heating a Wooden Splint
\begin{align*}NaCl\end{align*} and Water
Heating Copper
Heating \begin{align*}Cu(NO_3)_2\end{align*}
Solutions of \begin{align*}NaCl\end{align*} and \begin{align*}AgNO_3\end{align*}
Solutions of KSCN and \begin{align*}FeCl_3\end{align*}
Calcium Carbide and Water

## Energy Lab – Recognizing Potential Energy

Most of us intuitively know that a moving object has energy. As a result, we do not have trouble spotting examples of kinetic energy in the world around us. Recognizing potential energy, though, can be more challenging. In this lab, you will look at several examples of potential energy. In each case, you will prove that potential energy exists by converting the potential energy into kinetic energy. You must be careful to prove two points in each experiment:

1. You must prove that the potential energy is stored in the object itself. To do this you will have to be careful not to add any of your own energy to the object. You are not allowed to throw the object, or push the object, or pull the object. You are only allowed to release the object by removing your hands from the object.
2. You must prove that the object has potential energy by storing that energy for \begin{align*}10 \ seconds\end{align*}. To do this, you will hold the object still for a count of 10. Only after you have counted to 10 are you allowed to release the object.

Mini-lab One: Gravitational Potential Energy

When you hold an object above the Earth’s surface, the object has potential energy due to its position relative to the ground below.

Materials:

A marble sized chunk of modeling clay

Method:

Using two fingers, hold the modeling clay several feet above your desk, and count to 10. By counting to 10, you are proving that the energy can be stored and thus, that it is potential energy. When you have finished counting to 10, release the modeling clay by removing your fingers. The modeling clay will drop to the desk. Notice how the potential energy that the modeling clay had when you held it above the ground is converted into kinetic energy as soon as you remove your fingers.

Mini-lab Two: Magnetic Potential Energy

When you hold two magnets close to each other, they have potential energy due to their relative positions

Materials:

Two fairly large bar magnets with opposite poles painted red and blue

Method:

Part One: Hold the two magnets so that the red end of one magnet is almost, (but not quite) touching the blue end of the other magnet. Count to 10. By counting to 10, you are proving that the energy can be stored and thus that it is potential energy. When you have finished counting to 10, release the magnets by removing your hands. The magnets will attract each other and thus, will slide together. Notice how the potential energy that the two magnets had when they were held near each other is converted into kinetic energy as soon as you remove your hands.

Part Two: Hold the two magnets so that the red end of one magnet is almost, (but not quite) touching the red end of the other magnet. Count to 10. By counting to 10, you are proving that the energy can be stored and thus, that it is potential energy. When you have finished counting to 10, release the magnets by removing your hands. The magnets will repel each other, and will slide apart. Notice how the potential energy, the two magnets had when they were held near each other, is converted into kinetic energy as soon as you remove your hands.

Mini-lab Three: Elastic Potential Energy

When you stretch or compress a spring, it has potential energy due to the positions of the coils relative to each other.

Materials:

A large spring

Method:

Part One: Set the spring on the table in front of you. Using your thumb and forefinger, compress the spring as much as you can. When the spring is fully compressed, count to 10. By counting to 10 you are proving that the energy can be stored and thus that it is potential energy. When you have counted to 10, remove your fingers from the spring. The spring will bounce back to its normal length. Notice how the potential energy in the compressed spring is converted into kinetic energy as soon as you remove your fingers.

Part Two: Set the spring on the table in front of you. Using both hands, stretch the spring as much as you can. When the spring is fully stretched, count to 10. By counting to 10, you are proving that the energy can be stored and thus, that it is potential energy. When you have counted to 10, remove your hands from the spring. The spring will bounce back to its normal length. Notice how the potential energy in the stretched spring is converted into kinetic energy as soon as you remove your hands.

## Separating Mixtures: Extracting Iron from Breakfast Cereal

Brief description of demonstration

A \begin{align*}150 \ mL\end{align*} volume of breakfast cereal is ground in a Ziploc bag containing a magnet. The metallic iron present in the cereal adheres to the magnet.

Materials

• Breakfast cereal (Cheerios or Total works well)
• 1 quart Ziploc bag or larger
• Magnetic stir bar
• \begin{align*}250 \ mL\end{align*} beaker

Procedure

Measure about \begin{align*}150 \ mL\end{align*} of dry breakfast cereal into the \begin{align*}250 \ mL\end{align*} beaker. Add the cereal to the bag and add the magnet. A magnetic stir bar is preferred, because the iron is easily visible against the white plastic of the stir bar. Expel as much air as you can from the Ziploc bag before sealing it. Grind the cereal and the stir bar together thoroughly with your hands, and against a desktop if needed until the cereal is pulverized. Remove the magnet from the bag. Metallic iron can be seen adhering to the magnet.

Hazards

None

Disposal

Throw the cereal and bag away in the trash.

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