Matter, Physical & Chemical Changes

Questions & Investigations

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To understand the different ways Matter and Energy can change, you must first understand something really kind of radical.….

According to scientists, the total quantity of matter and energy available in the universe is a fixed amount!

This means there will never be any more or less matter and energy in the universe. Scientists when they talk about this say "matter and energy are conserved".

Ok, so the total quantity of matter and energy in the universe is conserved…. What about change? How can Matter and Energy be changed?

We'll start by looking at changes in matter, but as you'll see, it is not possible to talk about changes in matter without talking about adding or releasing energy.

Matter can be changed two ways, physically and chemically. Let's discuss Physical changes first.

Physical changes. Physical changes occur when matter changes from one state of matter to another state of matter by adding or losing thermal energy. In a physical change of state matter retains its original identity, it just changes the state of matter it is in.

For example: Imagine a beaker of ice sitting on a warm hot plate. As you watch the ice, this solid water makes a physical change of state to liquid water. (By way, Heat is defined as the transfer of energy from one substance to another. It is not a type of energy.)

The ice in the beaker gains energy to make the change of state to water. Thermal energy flows from the hotplate, to the beaker, then to the ice. The frozen water molecules begin to vibrate harder and harder. Eventually the wter molecules break the bonds with each other and the molecules begin to rotate and translate.

Once liquid, the liquid water molecules continue to gain energy and vibrate, rotate, and translate more. Eventually, all the water molecules gain enough energy and VRT more until each becomes water vapor. (All three states of water are still made of good ole H2O.)

Now imagine being able to capture all the water vapor evaporated in a big bag. Then imagine placing the bag in a freezer. Then the situation reverses. Energy is released from the water vapor to the freezer until water forms. Finally as even more energy is released, ice forms again. In fact, in this perfect system, you'd end up with the same mass of ice as you had in the beginning.

· So ok, when matter is physically changed from one state of matter to another, there is still the same amount of matter. The matter merely changes to a different physical state.

· One more important fact. The amount of energy needed to be added to change ice into steam is the SAME amount of energy that will need to be released from the steam to change it back to the same amount of ice. This is due to the Law of Conservation of Energy. The law requires that the energy change in freezing, be the reverse of the energy change in melting…. and similarily for making and reversing all other changes of state.

Chemical changes are different then physical changes. Chemical changes involve changing one or more substances to produce one or more entirely different substances.

Sometimes chemical changes require energy to be added to the chemicals to make a reaction happen. Sometimes chemical changes give off energy or take in energy! In fact, scientists used knowledge of different chemical changes to create packs of chemicals, that when mixed together become cold (Instant Ice Packs), or hot (Instant hand warmers), and even to give off light (Light Sticks)!

A classic example of a chemical change occurs when natural gas, Methane (a greenhouse gas), is burned with Oxygen.

In this reaction, Methane and Oxygen chemically change into Carbon Dioxide (a greenhouse gas), Water, and release lots of thermal energy in the process. That's what happens in your gas furnace when you heat your home.

Lets take a good look at this reaction two ways, with words and with chemical symbols..

Reactants

 

Products
Methane +
Oxygen +
Thermal energy
Produces
Carbon dioxide +
Water +
Particulate "Unburned" Matter +

Light & Thermal Energy

 

CH4 +
2O2 +
Thermal energy
=>
CO2 +
2H2O +
PM +

Light & Thermal Energy

1

molecule

2

molecules

To burn you need all three parts of the Fire Triangle!

=>

1

molecule

2

molecules

PM is usually not shown in chemical equations. Most reactions are shown as "perfect burns" which is not usually the case in real life!!

 

Note: 1. When one molecule of Methane is burned (reacts) with two molecules of Oxygen the products of the reaction are one molecule of CO2 and two molecules of H20.

2. Two entirely different substances are produced in this balanced reaction, but the same amount of matter remains! Let's check this by adding up the type and total of the atoms on each side of the equation.

Reactants =>
Products

Amount of Carbon atoms

C=1
C=1
The same

Amount of Hydrogen atoms

H=4
H=4
The same!

Amount of Oxygen atoms

O=4
O=4
The same!!

This shows an example of the Law of the Conservation of Matter. The Law states "During an ordinary chemical change, there is no detectable increase or decrease in the quantity of matter."

What about Energy? Well, energy can be changed into different forms but is "conserved" too! In fact, the Law of Conservation of Energy also states that "Energy cannot be created or destroyed, but can change its form."

Examples,

o Light energy can be converted into electrical energy (Solar Panel).

o Electrical energy changing into light energy (light bulb) and

o Potential energy can be changed into Kinetic energy. (Water in a pond, water over a falls.)

In any case, the total amount of energy at the end will be the same amount as one started with.

So, in a Chemical Change, when one type of molecule is converted into another type of molecule this change is always accompanied by the conversion of one form of energy into another form.

Look up at the equation above where Methane is burned with Oxygen. In the equation a little energy is added on reactants side of the equation while lots of energy is released on the products side.

If energy is "conserved", where does the all this energy come from (on the reactants side)? Well, energy is stored in the Methane's chemical bonds. The Carbon atom bonds tightly to the 4 Hydrogen atoms. So each Carbon to Hydrogen bond represents chemical energy stored ( stored = kinetic energy) in the methane molecule..

When Methane molecules "burn" with Oxygen the Hydrogen atoms break their bonds with the Carbon atom. When these 4 "bonds" are broken, vast amounts of thermal energy is given off.

The reaction for another hydrocarbon, Gasoline C8H18 (Octane), is very similar. When gasoline is burned, much more thermal energy is produced than when Methane is burned. That's because there are way more Carbon to Hydrogen bonds available to break in gasoline, so lots more energy is released. Engineers took advantage of this knowledge and used gasoline to power cars and trucks. Methane (natural gas) can be used to power cars and trucks too, but there is much less energy per molecule burned.. Burning gasoline gives lots more power, but produces lots more CO2, a greenhouse gas, for each molecule of gasoline burned. (8 molecules burning gas vs1 burning metane)

Physical and Chemical Properties: (note: Properties are different than changes.) Properties are characteristics an element possesses, like color or hardness. Scientists know each element has a characteristic set of Physical and Chemical Properties. These properties are used to identify elements and also for choosing materials for building, or to create a particular reaction, etc. Knowing about these properties offers distinct advantages to you!

a. Knowing the Physical Properties of a substance allows you to identify a substance by its characteristic properties and chemical composition. Some examples of physical properties are: physical state of matter at room temperature, taste, melting or boiling temperature, density, crystal shape, electrical and thermal conductivity, and specific heat.

b. Knowledge of the Chemical Properties of substances allows scientists to predict how a substance will react with other substances and what substances will be produced by the reaction. For example by knowing the properties of Iron and Oxygen you can predict that if you react Iron filings with Oxygen gas the end result will be reddish Iron Oxide.

Answer questions in complete, quality, & correct sentences on a separate sheet of paper. Ensure answers reflect the questions.

Physical and Chemical Change & Matter and Energy Questions

1. Explain if it is, or is not possible to create any more matter and energy in the universe.

2. What does conserved mean in this article?

3. What are two different ways matter can be changed?

4. What must be added or released from matter to cause a physical change?

Tell what the process for each type of change of state is called. (Think back….!)

5. 5 kilograms of ice is changed directly into steam.

6. 5 kilograms of steam is changed into liquid

7. 5 kilograms of ice is changed into liquid

8. 5 kilograms of liquid is changed into ice

9. 5 kilograms of steam is changed directly into ice

10. 5 kilograms of liquid is changed into steam

11. Are the changes of state above physical changes or chemical changes? Tell Why.

12. You have 5 kilograms of ice. You melt the ice and capture all the water. What will be the mass of the water? Why?

13. The water in #12 above is changed into steam. What will the mass of the steam be? Why?

14. It takes 720 calories of energy to change 1 gram of ice at 0ūC to steam at 100ūC. How many calories will be needed to change the 1 gram of steam at 100ūC back into ice? What science Law helped you answer this question?

15. Describe the difference between a Physical Change and a Chemical Change.

Example: A woodcutter, to keep himself warm creates the following reaction

C6H10O5 + 6O2 + Thermal Energy = 6CO2 + 5H2O + Light +Thermal Energy (+PM)

Or, in plain language

Cellulose (wood) + Oxygen +Thermal Energy = Carbon Dioxide + Water + Light & Thermal Energy (+ PM)

16. Does the example above show a physical or a chemical change? Tell Why.

17. If, in the example above, the Cellulose and Oxygen together had a mass of 10 kilograms, what will the total mass of the Carbon Dioxide and Water be after the reaction is complete? Why?

18. What Law allowed you to answer question 17?

19. The energy shown on the left (reactants) side of the wood burning equation is much less than the energy shown on the right (products) side of this equation. Where does all this energy come from?

20. Water has a boiling point of 100°C and a freezing point of 0°C. Tell if these are chemical or physical properties.

21. Knowledge of which type of property allows one to predict what will be produced when one substance reacts with another? .

22. Does a change from one form of energy to another cause a loss of energy? Tell Why.

23. Time to show what you've learned!

- Lets say your home's solar array receives 15 kilowatts of light energy a day.

- Your measurements indicate the array produces 9 Kilowatts of electrical energy and gives off 5 Kilowatts of thermal energy.

Explain if these measurements would be correct according to the Law of Conservation of Energy.

 

Part 1 Figure 1 - Conservation of Matter - The Ice + Water Investigation

a. Create a CQC figure for the investigation that shows:

i. The 3 phases of the investigation

ii. How the system gains and loses energy and where the energy comes from/goes.

iii. Label the mass and state of matter before melting, after melting, & after freezing again.

iv. Include DT1 on the bottom 1/4 of the Figure

v. Only use Averages from the data in your conclusion

Answer each question in complete quality and correct sentences that reflect the question on a lined paper attached to the Figure.

1. What question is this investigation seeking to answer?

2. What is the manipulated variable in this investigation?

3. What is the responding variable in this investigation?

4. What type of energy is gained or lost in this system?

5. What was done to improve the reliability of this experiment?

6. What was done to improve the Validity of this experiment?

7. Was this a chemical or physical change?

8. What is your conclusion? (Short Conclusion!!)

 

Part 2 Figure 2 - The CO2 Popper Demonstration; Changes and Energy in a System

a. Create a CQC figure for the demonstration that shows:

i. A "visible" drawing of the inside of the film can before, during, and at the final phase of the demonstration.

ii. How the system gains and loses energy.

iii. Show where the energy comes from/goes in the system.

iv. Label the state of matter before, during, after.

b. Answer each question in complete quality and correct sentences that reflect the question on a lined paper attached to the Figure.

1. What is in the film can at the start of the investigation?

2. What is the relative inside temperature of the film can immediately after the demonstration?

3. Where does the energy come from to cause the dry ice to change state?

4. Name the phase change the dry ice made.

5. Explain why the Dry ice (CO2 solid) inside the can caused the cover to come off violently.

6. Does the CO2 popper demonstrate a physical or a chemical change? Why?

7.What type of energy, kinetic or potential, is demonstrated when the bottom of the can blasted off?

8.What type of energy, kinetic or potential does the Dry Ice possess?

 

Part 3 Figure 3: The Piezo Poppers Demonstration - Changes and Energy in a System

a. Create a CQC figure for the demonstration that shows:

i. A "visible" drawing of the inside of the film can before, during, and at the final phase of the demonstration.

ii. How the system gets, creates more, and loses its energy.

iii. Show where the energy comes from/goes through the system.

iv. Label the state of matter before, during.

b. Answer each question in complete quality and correct sentences that reflect the question on a lined paper attached to the Figure.

1. What substances were inside the film can when you closed the lid?

2. What is the relative inside temperature of the film can immediately after the demonstration?

3. Where does the energy come from to start this reaction?

4. Where does the energy come from once the reaction starts?

5. Completely write out the reaction that occurred inside the film can .

6. Describe why the bottom of the film can was violently pushed off the top

7. Does the Piezo Popper demonstrate a physical or a chemical change? WHY?

8. What type of energy did the ethanol possess?

9. What type of energy occurred when the igniter was pressed?

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