Reading #1: Chemical vs. Physical ChangesMatter is changing all around us. . . whether matter rusts, boils, freezes, bakes in the oven, or gets digested in your

stomach, we are surrounded by changes every day! There are two main types of change: physical and chemical.

But how do we know what type of change is taking place?

Let’s start by describing physical changes. A physical change to an element or molecule will change the

appearance of the substance and will cause a change to some properties of the substance, but does not change its

chemical identity. For example, the size or shape may change but it is still the same substance with the same

number and types of atoms and no chemical bonds are broken. Additionally, physical changes can often be reversed

or undone by physical processes.

Examples of physical changes can be as simple as cutting, ripping or removing some mass from the substance. In

each case the size or shape of the substance has changed but it is still the same substance. Think about ripping a

piece of paper as an easy example. It is obvious that even

though it may be in pieces, it is still paper. Another example

of a physical change is a change to the state of matter.

Remember, a change in state of matter is also called a phase

change and can turn a solid to a liquid, a liquid to a gas and

so on. A phase change occurs when energy is added or

removed, changing the motion of the particles but not the

composition of the particles. If we use water as an example, it is still the same chemical composition, H2O,

even when it is frozen as ice or melted into liquid water or

vaporized into a gas. Water is the same chemical substance

no matter which state or phase it is in because phase changes

are just physical.

In contrast to physical change, a chemical change

results in the formation of one or more new chemical substances. A chemical change results in substances with a

Name __________________________________________________________ Period ________________

Notice in the phase change from ice to liquid water to water vapor, it is still made of only water molecules, but their motion and arrangement is different

Reading Packet – Unit Three ‘How can I make new stuff from Old

Stuff? ‘

different chemical identity because new chemical bonds are formed between the atoms of the original substances

and/or the chemical bonds of the original substances are broken. Chemical changes are not reversible and cannot easily be undone. A chemical change is often referred to as a “reaction” because the process can sometimes

be dramatic, creating unexpected odors, gases, temperature change or colors.

Some examples of chemical changes are combustion (burning), digestion of food, rusting, rotting and

baking/cooking food.

Let’s use combustion (burning) wood as an example. Even though wood is a mixture, it contains a lot of

carbohydrate molecules, which are mostly made of carbon, hydrogen, and oxygen. When the carbohydrate

molecules react with oxygen gas in the air, the end product is water vapor, carbon dioxide, and carbon that we see

as a charred black substance.

The soot is mostly Carbon

Both chemical and physical change lead to differences to the original substance(s). The difference between the two

types of changes lies in whether the change results in a whole new substance with rearranged atoms/molecules, or not. But changes to matter, whether chemical or physical, are what drive the processes of

Earth, space, and life!

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Reading #2: Different Properties – Different Substance As you read in the previous section, chemical changes result in a new chemical substance. But how can you tell if

the substance you end up with is really a different substance than you started with? One way is to know it’s

molecular structure and chemical formula. But what if you aren’t sure what the chemical formulas are? What can

you observe in the lab that will tell you if you’ve made a new substance?

Remember that in unit 2 we learned that different substances have different molecular structures, which gives them

different PROPERTIES!

Some properties are not helpful in showing that a chemical reaction has occurred, such as mass or shape of the

substance. Mass, shape, and state of matter can change, even if a new substance hasn’t been created. However, other properties can be examined to determine if a chemical reaction has occurred. Some of the properties

used to determine if there has been a chemical change are solubility, density, and melting point.

Substance Properties: Solubility If you sprinkle a little salt into a glass of water and stir, the salt seems to disappear. Instead of seeing pieces of salt

in the water, you see cloudy salt water. You do not see the grains of salt, because salt dissolves in water. Scientists

say the salt is soluble in water. However, salt does not dissolve in all liquids. When you determine if a substance is

soluble in a liquid, you are identifying another property of the substance. The property is called solubility.

Solubility is the capacity of one substance to dissolve in a liquid substance. The substance salt is soluble in water.

Solubility in water is a property of salt. Remember that substances have properties that are always the same for that substance. If solubility in water is a property of salt, then it must always be true of salt.

Where Does a Substance Go When It Dissolves? If you stir sugar into a glass of iced tea, the sugar will look like it has

disappeared. You know the sugar is still there because the tea tastes sweet. This is an interesting fact about

solubility. When a substance is soluble, it might look like it disappears in the liquid, but the substance is still there.

The substance breaks up into very small pieces that are too small for you to see. Sugar is soluble in water, and a

glass of iced tea is mostly made of water. The particles that make up the solid sugar move away from each other

and mix with the particles of the water. Iced tea is another example of a mixture. It is a mixture of water and tea.

Sweetened iced tea is a mixture of water, tea, and sugar.

Recall – what is a property again? Write the definition of a property in the space below…

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Substance Properties – Melting PointButter starts to melt at approximately 32.3°C or

90.1°F. This temperature is

called the melting point of butter. Melting point is

the temperature at which a solid substance starts

to become a liquid. A solid substance gets hot, but it

does not start to melt until it reaches its melting

point. Although a whole stick of butter would take

longer to melt than a small piece of butter because

there is more of it, the temperature at which each of

them starts to melt is the same!

Every sample of a pure substance has the same melting point.

For example, a tiny piece of pure gold and a large piece of pure gold have the

same melting point: 1,064oC (1,948oF)

A bathtub full of pure water and a glass of pure water have the same melting

point: 0oC (32oF)

A huge piece of pure iron or a little iron nail have the same melting point:

1,538oC (2,800oF)

And although butter is not a pure substance, we would expect a sample of the same type of butter, no matter

the size, would also have the same melting point.

Do All Substances Have Melting Points? If the definition of melting point is the temperature at which a solid

starts to become a liquid, it might seem strange to picture something like oxygen, a substance that is typically

a gas, having a melting point. But in fact, all pure substances have melting points. Let’s go back to oxygen for

a minute. Even though oxygen typically exists as a gas, if you could make the temperature really cold, you

could turn oxygen gas into solid oxygen. Once oxygen became solid, it could be melted into a liquid.

In everyday experience, however, the temperature is not cold enough to see oxygen as a solid. It is not even

safe or possible for your teacher to demonstrate this in the classroom. Unfortunately, it is difficult to

measure melting point in class so people must rely on scientists who have done these things to provide other

people with information.

Substance Properties - Density If you were sitting at a table and in front of you were a loaf of bread

and a cement block that were the same size, which one would be

heavier? You probably do not need to do scientific tests toanswer this

question. You could easily pick up theloaf of bread, but the cement block would be harderto pick

up. They take up the same amount of space (volume), but the amount of stuff or matter in them is different (mass).

Thinking about the bread and cement block may help you learn about another property of substances called density.

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Liquids and gases also have density but this reading will focus only on solids.

The relationship between mass and volume is what scientists call density. Density is the mass in a set volume of a substance. You may have heard the word dense before. When something is dense, it has a lot of mass for a little

volume. You could say that cement is denser than bread. The amount of mass for a set volume of cement is more

than the amount of mass for that same volume of bread. This mass-volume relationship is important because every pure substance has a specific mass-to-volume relationship. Every pure substance has a specific density. For

example, the density of aluminum is always 2.7g/mL

no matter how big or small the piece is.

However, density does not mean a substance is heavy or light. Instead, we could say it is a measure of how heavy

or light it is for its size. Sometimes an object is heavier than another

but not as dense because its not heavy for its size.Examples:

• Saturrn is much heavier than Earth but not as dense.

• A log is heavier than a pebble, but not as dense • A Nerf football is heavier than a marble, but not as dense

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Reading # 5 What Is a Chemical Reaction? Getting Ready Have you ever baked a cake? First you combine flour, sugar, eggs, and other ingredients. Then you pour the batter

in a pan and put it in the oven. When you take it out of the oven, it is a cake. Do you think the ingredients changing

into a cake in the oven are a chemical reaction?

Explain why you think baking a cake is or is not a chemical reaction.

In class you observed a chemical reaction when you mixed road salt and baking soda in water. Once the substances

combined, changes occurred. For example, you may have seen bubbles, the bag expanding, and a white solid form

that did not dissolve. These changes are evidence that a change, called a chemical reaction, occurred. A chemical

reaction happens when two or more substances combine with each other in a way that makes new substances form.

The substances are new because they are different from the substances you started with. The substances that you

started with changed into different substances.

How Can I Know Whether New Substances Formed? You may have learned that when substances are different, the properties of the substances are also different. If old

substances change into new substances, certain properties of the new substances will be different from the

properties of th e old substances. If substances have different chemical properties before and after a process, then a chemical reaction occurs. They are evidence of new substances that have different properties from the old

substances. Remember that to tell for sure whether a chemical reaction occurred, a scientist must test the properties

of the substances before and after a process. If a chemical reaction occurred, the properties of the materials will

have changed. This is what always happens in a chemical reaction.

There are also signs you might be able to observe that let you know if a chemical reaction has occurred; these are

unexpected color changes, unexpected odor changes, a rise or drop in temperature (that takes place even if the

substance isn’t heated up on a hot plate or cooled down with ice/freezer), formation of bubbles to indicate a gas has

formed, or formation of a new solid substance (called a precipitate)

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Reading #5 (continued)Chemical reactions occur all around you. They do not happen just in the laboratory or

in science class. Digesting food, rotting food, rusting, and burning are all chemical

reactions. Even on the 4th of July when you light a sparkler, you observe a chemical

reaction. Burning is always a chemical reaction, even though it does not always make

such a bright light as burning a sparkler. As a sparkler burns, the metal of the sparkler

and oxygen from the air interact and form a new substance. The reaction would take a

very long time if you just waited for it to happen. A flame adds energy to get the

reaction started quickly. Often something needs to happen to get a chemical reaction

started. Substances may need to be mixed or heated first. Even if you mix all the

right ingredients in the kitchen, they do not become a cake as they sit on the table. The ingredients need to be mixed

and cooked. Then they interact to become something new—a cake.

Reactants and Products in Chemical Reactions In a chemical reaction, the old substances that interact with each other to form new substances are called reactants. The reactants are the starting substances in a chemical reaction. It may help you to think about the reactants as the

substances that act or react together. In the sandwich bag experiment, the substances you started with in the bag

were the reactants. The products are the substances you ended up with at the end. They are the new substances.

A reactant is a starting substanceA product is the substance

in a chemical reaction. made by a chemical reaction.

Chemical EquationsWhen you write about a reaction, you are writing a chemical equation. A chemical equation is a way to represent

chemical reactions. The equations include plus (+) signs and an arrow. Notice that the reactants side of this

chemical reaction has a plus (+) sign. In a chemical equation, the plus sign means that the reactants are interacting.

The arrow could be though of as meaning “changes to”.

This chemical equation tells more about the atoms and molecules of each substance. You can see the number of

atoms and the types of atoms. You can see the number of molecules and the types of molecules. You can see which

atoms and molecules react and what they form. A chemical equation can help you understand what is happening to

the old substances and new substances in a chemical reaction.

The following is the chemical equation for burning magnesium in sparkler

2 Mg + O2 2MgO1 molecule of oxygen 2 molecules of magnesium oxide

2 atoms of

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the element magnesium

Notice that there are the same number of magnesium atoms on the reactant side and the product side (2 magnesium

atoms on each side). And there are 2 oxygen atoms on each side. That is because a chemical reaction never destroys

or creates atoms, it just rearranges the atoms in a new way.

Reading #6: TYPES OF CHEMICAL REACTIONSAll chemical reactions involve one or more reactants that are changed into one or more products when the atoms are rearranged. Some chemical reactions involve breaking bonds, some involve making bonds, and some involve both. Here are several different types of chemical reactions:-Decomposition-Synthesis-Single Replacement-Double Replacement

I. DECOMPOSITION REACTIONSDecompose=to break down. This might be helpful when thinking about chemical reactions that are known as decomposition reactions.

A decomposition is one of the most common types of chemical reactions. In a decomposition reaction, the bonds of a single reactant are broken apart and the products are made of the reactant’s component pieces. A decomposition reaction will have a single reactant and two or more products.

A decomposition may occur in a single step or multiple ones. Because chemical bonds are broken, a decomposition reaction requires the addition of energy to begin.

The reaction could be represented by the following:AB → A + B

A real chemical equation example is water breaking apart:

2H2O 2H2 + O2

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Reading #6 (continued)

SYNTHESIS=

To make; to build; to put together.Look at the picture of Los Angeles, California to the right. The beautiful blue sky is being taken over air by a layer of thick, hazy smog (so sorry you don’t have a color copy )Smog is a serious form of air pollution that can irritate the eyes and throat and trigger asthma. One of the major components of smog is the molecule nitrogen dioxide, a toxic gas with a sharp odor. But where does this gas come from? It forms when a molecule called nitric oxide, which comes from sources such as car exhaust, reacts with oxygen in the air. This reaction is a synthesis reaction.

What Is A Synthesis Reaction? A synthesis reaction occurs when two or more reactants combine to form a single product. A synthesis reaction can be represented by the general equation:

A + B → AB

In this equation, the letters A and B represent the reactants that begin the reaction, and the letter AB represents the product that is synthesized in the reaction. The arrow shows the direction in which the reaction occurs.

The chemical equation for the synthesis of nitrogen dioxide (NO2) from nitric oxide (NO) and oxygen (O2) is:

2NO + O2 → 2NO2

WHY CAN’T A SYNTHESIS REACTION BE USED TO MAKE WATER by Anne 9

Marie Helmenstine, Ph.D.Water is the common name for the dihydrogen monoxide or H2O. The molecule is produced from numerous

chemical reactions, including the synthesis reaction from its elements, hydrogen and oxygen. The balanced

chemical equation for the reaction is: 2 H2 + O2 → 2 H2O

How To Make Water

In theory, it's extremely easy to make water from hydrogen gas and oxygen gas. Simply mix the two gases together,

add a spark or sufficient heat to provide the activation energy to start the reaction, and presto! Instant water. Merely

mixing the two gases together at room temperature won't do anything. Energy must be supplied to break the

covalent bonds that hold H2 and O2 molecules together. When the chemical bonds reform to make water, additional

energy is released, which propagates the reaction. The net reaction is highly exothermic.

Understanding the Reaction

French chemist Antoine Laurent Lavoisier named hydrogen (Greek for "water-forming") based on its reaction with

oxygen (another element Lavoisier named, which means "acid-producer").

Lavoisier was fascinated by combustion reactions. He devised an apparatus to form water from hydrogen and

oxygen to observe the reaction. Essentially, his set-up employed two separate bell jars (one for hydrogen and one

for oxygen), which fed into a separate container. A sparking mechanism initiated the reaction, forming water. You

can construct an apparatus the same way, so long as you are careful to control the flow rate of oxygen and hydrogen

so you don't try to form too much water at once (and use a heat- and shock-resistant container).

Why Can't We Just Make Water?

A 2006 report by the United Nations estimated about 20% of people on the planet don't have access to clean

drinking water. If it's so hard to purify water or desalinate seawater, you may be wondering why we don't just make

water from its elements. The reason? In a word... BOOM.

If you stop to think about it, reacting hydrogen and oxygen is basically burning hydrogen gas, except rather than

using the limited amount of oxygen in air, you're feeding the fire. During combustion, oxygen is added to a

molecule, which produces water in this reaction. Combustion also releases a whole lot of energy. Heat and light are

produced, so quickly a shock wave expands outward. Basically, you've got an explosion. The more water you make

at once, the bigger the explosion. It works for launching rockets, but there are times where that went horribly

wrong. The Hindenburg explosion is another example of what happens

when a lot of hydrogen and oxygen get together.

So, we can make water from hydrogen and oxygen, and in small quantities,

chemists and educators often do make it. It's just not practical to use the

method on a large scale because of the risks and because it's much more

expensive to purify hydrogen and oxygen to feed the reaction than

it is to make water using other methods or to purify contaminated water

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Reading #6 continued

III. Replacement Reactions

A replacement reaction is a bit how it sounds-something is going to replace something else. There are two different types: single replacement and a double replacement.

SINGLE REPLACEMENTIn a single replacement reaction, a single uncombined element replaces another in a molecule; in other words, one element trades places with another element in a molecule. These reactions come in the general form of:

AB + C → A+ CB

An example is the reaction between zinc and hydrochloric acid. Notice how hydrogen is bonded to chlorine in the reactants, but in the product zinc replaces hydrogen to pair with chlorine to form zinc chloride.

Zn + 2HCl ZnCl2 + H2

DOUBLE REPLACEMENTIn a double replacement reaction, a positively charged atoms (cation) from one molecule and the negatively charged atom (anion) from another molecule switch places and form two entirely different substances. A double replacement could almost be thought of as two atoms trading places.These reactions are in the general form:

AB + CD AC + BD

An example equation would be as follows:2KI +Pb(NO3)2→2KNO3+PbI2

(Notice how NO3 (nitrate) and I (iodine) switch places)

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Reading #7 –Is Creating a Mixture a Chemical Reaction?If you had a glass of clear water and you poured red drink powder in it, the liquid

would turn red. Did a chemical reaction occur? The following questions will help you

think about whether this is a chemical reaction.

1. What observations could be evidence that a chemical reaction occurred?

2. What must happen to the atoms and molecules of the substances for this to be a

chemical reaction?

This reading will help you think about whether mixing drink powder in water results in a chemical reaction or not.

Do Atoms Always Rearrange? A can of soda fizzes when you open it, but that is not a chemical reaction. When you boil water, it bubbles, but that

is not a chemical reaction. You learned that bubbles might be evidence that a chemical reaction occurred. These are

two examples when bubbles can fool you.

How can you tell when a chemical reaction results in new substances and when substances are mixing, but not

changing into new substances?

Two different things can happen when you mix substances together. One, the atoms arrange in new ways to create

new substances. This is a chemical reaction. Two, the atoms and molecules do not rearrange. They do not interact

chemically to create new substances. For example, in mixing a glass of chocolate milk, the atoms and molecules in

the chocolate and the milk all stay next to each other in the glass, but they do not break apart and recombine. In this

circumstance, you have created a mixture. A mixture is not a chemical change.

Comparing Phase Changes, Mixtures, and Chemical Reactions

The following chart is one way to organize what you have learned about the differences among phase changes,

mixtures, and chemical reactions.

Reading #8:THE MASS OF MATTER

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Comparison of Phase Change, Mixture, and Chemical Reaction

Process Before the Process After the Process Atoms and Molecules

Phase Change 1 substance Still have the same substance

Move closer together or farther apart, speed up or slow down

Mixture 2 or more substances Have the same 2 or more substances that you started with

Atoms do not rearrange to form new substances.

Chemical Reaction 1 or more substances

Have 1 or more different substances than the ones you started with

Atoms break apart and rearrange in new ways to form new substances.

Antoine Lavoisier (1743–1794) Matter may change from a solid to a liquid. Elements may react together to form compounds. What happens to the mass of matter in a bowl of water when it is left to stand in the hot sun? What happens to the mass of matter in a piece of paper when it is burned? Sometimes in situations like this it seems as if matter is disappearing. But the disappearance of matter is an illusion. Matter may change from one form into another. For example, when the water in the bowl absorbs energy from the sun and evaporates, it becomes water vapor in the atmosphere. The piece of paper gives off heat and light energy as it burns, and the matter in it is converted into carbon dioxide, water vapor, and other gases that escape into the atmosphere. Some of the mass will remain behind as ash. In both cases, the matter changes its form, but its total mass stays the same. The same mass of each element is present before and after the change. Matter is neither created nor destroyed during these changes.It took early scientists hundreds of years of scientific study before the law of conservation of mass became accepted. For a long time, scientists had suspected that matter could not be created or destroyed, but nobody had performed an experiment that proved it. During the late 18th century, French chemist Antoine Lavoisier and his wife Marie-Anne conducted several experiments that demonstrated the conservation of mass. Antoine was famous for his accurate observations and insistence on careful measurements. He used accurate balances that could measure very small changes in mass during his experiments.

Many of the Lavoisier's experiments were conducted in sealed glass containers from which matter could not escape or enter. For example, in one experiment, Antoine put fruit into a sealed container, measured its mass, and then left it in a warm place for a few days. The fruit rotted and changed into a putrid mess. Gas was released from the decomposing fruit and droplets of water formed on the glass, but nothing escaped from the container. Lots of changes had taken place, but the mass of the sealed container and the rotten fruit was equal to the mass measured at the beginning of the experiment. 

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In other experiments, Antoine heated elements in enclosed containers with air inside them. He discovered that new substances were formed but that the container and its contents had the same mass as they did before heating. When he measured the mass of the new solid substances he had made, he discovered that they were heavier than the original elements he heated. In this way, he determined that they must have gained their mass from the air. On the basis of these experiments, he also concluded that air contained several gases, one of which reacted with the elements in the experiment. He called this gas oxygen (which had previously been discovered and described—but not named—by Carl Wilhelm Scheele and by Joseph Priestley).

In 1789, Antoine wrote the best textbook on chemistry the world had seen. In it, he introduced a new scientific law that he called The Law of Conservation of Mass. This law stated that in any closed system (as small as a sealed container or as big as the whole universe!) the total mass remains the same, regardless of what changes take place inside.

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READING #9: BALANCING EQUATIONS:

In everyday language, people say that an object rusts. Now you know that the scientific name for rust is oxidation.

You now know that not only do the type of atoms in a chemical reaction stay the same, but the number of atoms

also stays the same because mass is always conserved.

You can look at the number of atoms involved in the process of rusting as an example of this.

The chemical reaction that causes rusting can be written as the following chemical equation:

iron + oxygen → iron oxide.

Another way to write the equation is to use the chemical formulas: 4Fe + 3O2 → 2Fe2O3.

Using the chemical formulas, you can count the atoms on each side of the arrow to be sure that the number of atoms

is the same. When the number and type of atoms are the same on both sides, scientists call the equation balanced.

The number in front of the element or compound tells you how many atoms or molecules you have. In the

preceding equation, the 4 in front of the Fe means there arefour atoms of iron. The subscript in the oxygen (O2)

means there are two oxygen atoms in every molecule of oxygen. All together, there are four iron atoms (Fe) and six

oxygen atoms (O) on each side of the arrow. The atoms are arranged differently, but they are all still there. The

equation balances because of the principle of conservation of mass. In a chemical reaction, the atoms rearrange, but

the number of atoms always stays the same.

Why Does Mass Stay the Same in a Chemical Reaction? Mass stays the same in a chemical reaction because the same atoms that are in the reactants rearrange to form the

products. All the atoms are still there, so the mass stays the same before and after the reaction.

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