Name_________________________________________________________ Period _________

Reading #1:The Nature of MatterEssential Question: What is matter? IntroductionMatter is anything that has mass, volume, and is made of particles called atoms. A person, car, dog or cat, water, and even the air you breathe are matter because they all have mass, volume, and are made of particles called atoms.

Matter can exist in four main states: solid, liquid, gas, and plasma. We will learn more about states of matter later in our chemistry unit.

However, some things are not matter. For example, forms of energy, such as light and sound, forces such as gravity and friction, and abstract things such as ideas and memories are not matter because they don’t have mass, volume, and are not made of atoms. But the physical things around you- the things you can feel, hold or touch- are matter.

Chemistry is the branch of science that studies types of matter, how it changes, and how matter interacts with other matter.

Building BlocksAtoms, which are the building blocks of matter, are a lot like Legos. Just like there are a lot of types of Legos, there are a lot of different types of atoms. Just like building with Legos, atoms canbe put together to build different things; some atoms join

READING PACKET – UNIT TWO ‘HOW CAN I SMELL THINGS FROM A DISTANCE?’

If we could look closely enough, we would see that all matter is made of particles called atoms

together to build matter that is simple and some atoms join together to build matter that is more complex.

Atoms Try this! Take a post-it note from your supply box and tear it in half. Take ONE of those halves and tear it in half. Take one of those halves and tear it in half, making a smaller and smaller square until you can’t tear it anymore. Compare each tear to the chart at the bottom of your page! (Now clean up all your scraps!)

How many times could you tear the paper? If your were able to tear it even ten times, you would still need to tear it a twenty more times before it were the size of an atom! The word atom was coined in 440 bc, by a Greek philosopher. It means ‘un-cuttable’ in Greek, because an atom is the smallest piece of something that is still that thing. An atom of gold is the smallest amount of gold you could possibly have and still have gold. All matter is made up of atoms. They are the VERY SMALL particles that build everything around us, whether it’s solid, liquid, or gas.

For a very long time, scientists thought that an atom was the very smallest thing there could possibly be. In the last century, scientists have discovered that there are even smaller particles that make up atoms, called protons, neutrons, electrons. However, an atom is still the smallest unit of a substance that has the characteristics of the substance. Even though you could break an atom of gold into smaller pieces, those pieces would no longer be ‘gold’.

Comparison ChartCut # Metric length Standard

lengthComparable Object

0 7.0 cm 2.75” (post it note) Finger & toe length

3 3.5 cm 1.38” Eye4 1.75 cm 0.69” Keyboard keys6 0.44 cm 0.17” Poppy seeds8 1mm 0.04” Thread. I’d be amazed if you

are still cutting!

How small is small?

An atom is VERY tiny, but what does that mean? A block of gold this size Would contain over 1,077 SEXTILLION atoms. That’s 1,007,000,000,000,000,000,000,000 atoms! It would take you more than a lifetime to draw that many atoms! Even the period at the end of this sentence is as large as 7.5 TRILLION atoms.

10 0.25mm 0.01” Still cutting? Most have quit by now

12 0.06mm 0.002” Human hair width14 0.015 mm 0.006” Width of paper, microchip

components18 1 micron 0.0004” Water purification openings,

bacteria19 0.5 micron 0.000018” Visible light waves24 0.015 micron 0.0000006” Cell membranes31 0.0001 micron 0.000000004

5”Atom

Reading #2 – Elements and the Periodic Table

Essential Question : What is an element, and how are elements organized in the periodic table?

The Alphabet of Matter Do you remember when you first learned to write your name? It may have been a VERY challenging exercise! Before you could manage something complicated like Aiden or Hayley or Elizabeth, you first had to learn how to make each individual letter! Letters are the building blocks for words, which are the building blocks for paragraphs, essays, and novels. In English, just 26

letters can be combined into over 200,000 different words. Elements are the building blocks of matter in the same way that letters are the buil ding blocks of words. Building matter is similar to building words except instead of starting with 26 letters, we start with 118 elements. These elements can be

arranged in billions of different combinations to make all the matter that exists!

What is an Element?An element is a pure substance, made of only one type of atom. An element cannot be broken into anything simpler by any natural means. All the atoms of a given element have the same number of protons in their nucleus. Helium is an element, so in a helium balloon all of the atoms would be helium atoms, and they would all have 2 protons in their nucleus. Gold is an element, so in a sample of gold all of the atoms would be gold atoms, and they would all have 79 protons in their nucleus.

Organizing the Elements We always write our alphabet in the same order. The letters in our language are organized alphabetically. The 118 elements in our universe are

arranged in a chart called the periodic table. This table is organized according to the number of protons in each element’s nucleus. (the atomic number tells you the number of protons in an atom’s nuclueus) Hydrogen, with only one proton, is the first

element on the table. The second element has two protons, the third element 3 protons, and so on until you reach the 118th element, which has 118 protons! Because protons make up a big part of the mass of the atom, the periodic table is also organized by atomic mass, with the lightest elements at the beginning and the heaviest at the end. You read the periodic table from left to right and from top to bottom, so helium is our lightest element and ununoctium is the heaviest.

Organizing by Properties Today, we see the periodic table as mainly organized based on number of protons. But the person who first designed the periodic table didn’t even know what a proton was! Back in 1868, a scientist named Dmitri Mendeleev arranged the elements based on atomic mass, and based on properties. A property of matter is a characteristic that can be used to describe it. For example, if you were to describe helium you might say it was a gas (at room temperature), that it is colorless, odorless, that it is very light, that it’s not flammable and that it has a strange effect on vocal cords! All of these things are properties of helium. If you tried to describe gold, you would come up with a very different list of properties. You might say that it was a solid (at room temperature), that it is yellow in color, shiny, bendable, very dense, and soft relative to other metals. These are all properties of gold.

We are Family Mendeleev used the known properties of the elements to group similar elements together. He began arranging them into groups called families that all share similar properties. For example, Helium, Neon, Argon, Krypton, and Xenon, which are all on the far right side of the table, are members of a family called the noble gases. They are all colorless and odorless, gases at room temperature, and they are all non-reactive, which means that they don’t bond with other elements to form molecules. On the other side of the table you’ll find Lithium, Sodium, Potassium, Cesium, and Rubidium. Members of this family, the Alkali metals, are mostly soft, silvery metals that conduct electricity and are HIGHLY reactive,

meaning they easily bond with other elements to form compounds. In fact, it is rare to find these elements by themselves in nature.

What Elements Do I Know? In the periodic table, each element is listed by its name and its chemical symbol.

The element oxygen has a capital O as a symbol, which makes sense for oxygen. But not all chemical symbols are so obvious. Below is a list of a few elements that can be used to make jewelry. Find each one in the periodic table and write its chemical symbol. As you can see, the symbol does not always match the name of the element. This is because when the period table of the

elements was created, Latin was the language scientists used. The Latin name for iron is ferrum. Iron’s chemical symbol is Fe. Elements that were named long ago still keep their Latin symbols. Reading #3: Molecules In Reading #2, you learned about substances called elements, which are made from one type of atom.A different type of substance made from atoms is called a molecule. Molecules are made of two or more atoms joined together through chemical bonding. Chemical bonds are created during chemical reactions and can be broken by chemical reactions as well. However, physical processes such as cutting, smashing, boiling or freezing are not enough to form or break the bonds of a molecule.

Some molecules are made of the same type of atom bonded together, such as oxygen gas, which is made of two oxygen atoms.

However, some molecules are made of 2 or more different types of atoms bonded together. A molecule that is made of two or more different types of atoms is also called a compound. Water is an example of a compound since it is made of 2 different type of atoms, hydrogen and oxygen. It takes two atoms of hydrogen and one atom of oxygen to make on molecule of water. Molecules are tiny particles with billions of water molecules in a single drop. According to NASA, “there are 120 times more water molecules in a cubic inch of water than there are stars in the observable universe” (Of Stars and Drops of Water)

All molecules have very different characteristics from the individual elements that make it. A great example is table salt, which is made of 1 sodium atom and 1

Element Symbol

Gold Nickel Silver Platinum

chlorine atom. Individually, sodium is a highly explosive substance and chlorine is poisonous; but when they chemically bond they form an edible substance that we use to make food taste better.

The parts of a molecule can be thought of as a recipe, with different ingredients combining to make a new product. However, this is a recipe that can’t change amounts. . . in a molecule, the number and type of atom is always the same and in the same proportions, otherwise you have a different substance.

A chemical formula is used to show the number and kinds of atoms present in a molecule. The type of atom is given using element symbols. The number of atoms is indicated by a subscript following the element symbol, unless there is only one of the atom in which no subscript is used.CHEMICAL FORMULA EXAMPLES

There are two hydrogen (H) atoms and one oxygen (O) atom in a molecule of water. The chemical formula is H2O

There is one carbon atom (C) and four hydrogen (H) atoms in methane. The chemical formula is CH4

There is one sodium atom (Na) and one chlorine atom (Cl) in one molecule of sodium chloride, commonly called table salt. The chemical formula is NaCl.

Reading #4 What Kind of Particles do I Breathe

Reading #5 What Gases Make Up the Air We Breathe?The Earth’s atmosphere is a layer of gas held in place by gravity, which prevents it from escaping into space. It protects life by

absorbing UV radiation, by holding in heat to warm the Earth’s surface and by reducing temperature extremes between day and night. The gases that comprise the atmosphere are commonly referred to as air, which is what all living things on Earth breathe. Air is a mixture, composed of several different molecules:

NITROGEN: ABUNDANT AND INERTIt’s a common misconception that oxygen is the most abundant gas in the air breathed on Earth; that honor goes to nitrogen, which makes up 78 percent of the air. Nitrogen occurs as N2 — two nitrogen atoms bonded together. The bond between them is very strong. Although inhaled nitrogen passes into the bloodstream, it is not used by the cells in the body. However, since nitrogen is essential for life — it is found in RNA, DNA and proteins — it must be chemically converted to be used by animals. One way this happens is through nitrogen fixation in plants.

OXYGEN: LIFE-GIVING GASMaking up almost 21 percent of the air all living things breathe, oxygen is absorbed by the lungs, or lung-like structures in lower animals, and transported to all cells in the body by the blood. Oxygen is the most unstable, and therefore the most chemically active, gas found in air. Although all animals need oxygen, it can be deadly in higher-than-normal concentrations: Breathing pure oxygen for extended periods leads to oxygen toxicity. In addition to its role in biology, oxygen is essential for combustion, the chemical process responsible for fire.OTHER GASESThe third-most abundant gas in the air on Earth is argon, but it only makes up less than 1 percent of air. Argon is classified as a noble gas in chemistry, meaning it is

Constituent Chemical symbol

Mole percent

Nitrogen N2 78.084Oxygen O2 20.947Argon Ar 0.934Carbon dioxide CO2 0.0350Neon Ne 0.001818Helium He 0.000524Methane CH4 0.00017Krypton Kr 0.000114Hydrogen H2 0.000053Nitrous oxide N2O 0.000031Xenon Xe 0.0000087Ozone* O3

trace to 0.0008

Carbon monoxide CO trace to

0.000025Sulfur dioxide SO2

trace to 0.00001

Nitrogen dioxide NO2

trace to 0.000002

Ammonia NH3trace to 0.0000003

very stable and seldom reacts with other compounds. There are several additional gases present in the air. These gases are referred to as trace gases and include water vapor, carbon dioxide, methane, helium, hydrogen and ozone. These gases are important components of our air, but are present in VERY tiny amounts. The CO2 we breath out with each breath makes up only .04% of the air! Water vapor makes up even less, but can increase on high humidity days.

Reading #6 – Three Forms of Matter—Solid, Liquid, and Gas

Think about eating a bowl of cold cereal for breakfast. What types of matter would be part of your breakfast? Are there any solids? Are there any liquids? Are there any gases? In

the box below, list the type of matter and the state of matter it is in. You may have identified matter in three forms— solid, liquid, and gas. Scientists call each form a state of matter. A state is the physical form in which a material can exist. As you read, think about the essential question: How can you tell which state of matter a material is in? and underline ideas that can help you decide.

What Determines the State of Matter a Material Is In? You live in a world of solids, liquids, and gases. You breathe in a gas, and you breathe out a gas. You eat solid matter. You drink liquid matter. As you have been thinking about matter, you have been considering the state in which you usually find each material. States of matter can change when matter gains or loses energy by heating or cooling. However, you usually find materials at room temperature. It is probably helpful for you to just think about room temperature as the temperature around you as you sit in your classroom.

Almost all materials can exist in solid, liquid, and gaseous form. However, we most often refer to a material’s state as the state in which it exists at room temperature. We think of butter as a solid, even though it can easily be melted to become a liquid. We think of Carbon Dioxide as a gas, although if it is cooled down enough it becomes solid dry ice.

Properties of a Solid: Can You Grab It, Hold It, or Poke It with Your Fingers? You can determine what state a material is in based on its characteristics. A fork is a solid. An apple is a solid. A rock is a solid. You can hold each of these solids in your hand. You can grab a piece of each of these things. You cannot grab and hold a piece of the air. You cannot grab and hold a piece of milk. You can grab and hold a piece of wood. Apples, rocks, and wood are matter in a solid form.

Here is another test. If you had a big glass bowl and you put a solid into the bowl, the solid would stay in its original shape. A rock would sit in the bowl and look like the same rock. Solids have a fixed shape. Fixed shape means that they stay the same until you do something like break or crush them. Another way to think about solids is that you cannot poke your finger into them. Push your finger against your desk or tabletop. It is a solid. Your finger will not go through it. Floors and walls are solids. A glass bottle, a plastic bottle, and a soda pop can are solids. Sidewalks, driveways, and roads are solids. Poking your finger into something is not a perfect test, but it can help you with the idea of many solids. You will be learning more in this unit about why you cannot poke your finger into most solids but can poke your finger into liquids and gases.

Solids have a fixed shape because the molecules that make up solids are very close together, and they don’t move much. This lack of particle motion is why it can be difficult to change the shape of a solid or put your finger through one. The particles are too tightly packed to let another object through or flow around in a container. This also means that solids are typically the most dense of the states of matter. Density is how much matter is in a given volume. Even a small sample of a substance that was very dense would feel very heavy (think: Gold). Even a large sample of a substance that has low density might feel very light (think: Helium). If you filled a balloon with solid gold and a balloon with gaseous helium, you can imagine which would have more mass! This is because gold is much more dense than helium.

Properties of a Liquid: Does It Change Shape When You Pour It? Liquids do not have a fixed shape. That means they do not hold the shape they are in. In the picture, you can see that the milk is in one shape as it pours out of the jug and a different shape in the glass. You could do this at home.

Measure one cup of liquid water (or milk) and pour it into a tall glass. Then measure another one cup, and pour it into a short glass. You will notice that the liquid in the two glasses is in the shape of the glass. Someone might be fooled and think that there is more liquid in the tall glass. However, what really is happening is that the liquid water takes the shape of the glass and fits into it. It spreads out more in the wide, short glass, so it might seem like less liquid. Liquids take the shape of the container they are in. They do not hold the same shape when you pour them.

We notice that liquids flow and fill containers because the particles that make up a liquid are typically farther apart than the particles in a solid, and they can move around a little bit more. This added space between particles, and the additional particle motion, is what gives liquids their characteristic ‘flow.’ It also means that most liquids tend to be slightly less dense than solids, because the particles are more spaced out, so there is less mass in the same amount of space. However, the particles in a liquid still tend to stick together, which is why liquids take the shape of their container, but don’t spread out to fill the container up. Because they don’t spread out, we say that liquids have a fixed volume

Properties of Gases Gases can be difficult to study because you cannot see most of them. However, gases are all around you. Gases do some of the same things that liquids do. You have already learned that air has volume; it takes up space. When air takes up space, it also takes the shape of its container. The difference is that a gas will fill up all of the available space in a container. If you poured a glass of water on the floor of the classroom, it would stay in a puddle wherever you poured it. If you spritz perfume into a room, however, the gaseous perfume will spread out until it is all around the room. Gases don’t have a fixed shape OR a fixed volume!

A room is like a big container. The air in the room you are in right now is taking the shape of the room. It is filling every corner. If you are reading outdoors or in a car, air is filling that space too. Everywhere you look there is air, even though you cannot see it. All types of gases take up the space of their containers. When gases fill the space of a container, gases also take the shape of the co ntainer. If you had a balloon in the shape of a star and you filled it with air, the air would

spread into the star shape and fill it to each point. When a material is in the gas phase, it has characteristics that are similar to air. The same thing would happen if you filled the balloon with a different gas, such as helium gas. You have probably seen helium- filled balloons in many shapes. Gases fill the available volume of their container.

Unlike solids and liquids, the particles that make up a gas can move VERY far apart, and they have a lot more energy. This means they move around much more than particles in a liquid or solid. This is why a small spritz of smelly perfume in the gaseous form can move all the way around the room. The particles don’t need to stick together, they can spread out to fill the space. This big space between particles means that gases are typically much less dense than liquids or solids.

Reading #7: What Needs to Happen to a Material so that I Can Smell It?

What Is the Difference between States of Matter and Phases of Matter? You have learned that solids, liquids, and gases are called states of matter. They can also be called phases of matter. When two different words are used to describe the same thing, it can be confusing. Outside of science class, people also have more than one name for things. For example, they use couch and sofa to describe the same piece of furniture. In science, state of matterand phase of matter both refer to the physical forms that matter can be in.You are studying three states or phases: solid, liquid, and gas.

When Are the Characteristics of Solids, Liquids, and Gases Important? People use the characteristics of the states of matter and phase changes in ways that you might not think about. One example is making candles. People who make candles use the characteristics of solids and liquids to create different shapes and sizes. First, they melt solid wax to make a candle. Things melt when a solid material turns into a liquid material—when it changes phases. The process of melting is called a phase change. Phase changes involve a change in thermal energy (heat) that cause the particles of the substance to move faster or slower, resulting in a different state of matter. When candle wax is liquid, it is easy to pour and can be poured into a container. The liquid wax takes the shape of the container it is poured into. Then the wax freezes, which is another phase change. When the liquid material turns back into a solid material, it goes through a phase change called freezing.

What is Really Meant By Freezing or Frozen?The process of freezing allowed the liquid wax to become a solid candle. But you probably know that candles do not need to be frozen in a cold freezer to keep their shape. They can sit on tables at room temperature. This is another time that a word you use outside of science class might confuse you. Scientists eat frozen ice cream, just like you. Scientists also put liquid water in the freezer to turn it into ice cubes. Scientists might describe winter weather as freezing cold. However, scientists also have a more precise meaning for freezing that is not about being cold. Freezing is the name for the phase change from the liquid to solid state. For some substances, like candles, they are considered frozen even though it is only room temperature. If

you can you think of other substances that are solid, or frozen, at temperatures that aren’t “freezing cold”, list them in the box:

What are Some Other Phase Changes?Freezing and melting are two phase changes that take place between solids and liquids and are easy to see in our every day lives. But what about other phase changes, such as those involving gases? The processes that change a substance into a gas is called vaporization. You have probably heard the term vaporized to refer to something “disappearing”. Of course it doesn’t disappear, it just turns to a gas and it can’t be seen anymore. Here are two ways that vaporization can happen:

1) Evaporation in which particles on the surface have enough energy to escape & become a gas

2) Boiling in which a substance is rapidly heated to a boiling point, transforming large number of particles into the gas phase.

Believe it or not, gases can sometimes form directly from solids without first passing through the liquid phase. When a solid changes directly into a gas, the process is a type of vaporization called sublimation. The most familiar example of sublimation is dry ice. Dry ice is solid carbon dioxide, which needs a very low freezing point (-78.5oC or -109.3oC) to stay solid. However, when dry ice is put at room temperature, it doesn’t melt into a liquid. It sublimates into a gas, which is used to make very cool special effects at Halloween!

Of course, gases can also turn back into solids and liquids. When a gas turns into a liquid, it is called condensation. The best example of this is when you get out of a hot shower and the mirror is all wet. This happens because the water vapor (gas) that formed from the hot shower hits the cool mirror and turns into a liquid. Gases can also turn directly into solids, skipping the liquid phase. When this happens it is called deposition. An example of deposition is when frost forms. As the temperature gets cold enough, particles of water vapor in the air slow down so much they become solid frost. We also saw deposition in the menthol lab. The

menthol vapors in the beaker turned into solid menthol on the bottom of the watch glass without becoming a liquid first.

Why do phase changes happen?When a solid becomes a liquid or when a liquid becomes a gas, it requires a lot of thermal energy. Thermal energy changes when heat is transferred from a warmer substance to a cooler substance. The energy affects the particles so that they will start to vibrate enough to slide past each other and then move so much they can escape. When going in reverse, from a gas to a liquid and a liquid to a solid, some thermal energy is lost. When the temperature drops, energy will be transferred from the gas atoms into the cooler environment. The particles will move slower and get closer together until a liquid forms and then even slower and closer together until a solid forms

More About Particle MotionImagine the billions of particles moving in one tiny bit of air. The molecules that make up the air are always moving. They move until they hit each other. Then they bounce off and go in a different direction. Air particles never stop moving. They are always bumping into each other and bouncing off. Even though particles never stop moving, particles move at different speeds. Particles in a gas move much faster than cars can move. The average speed of air particles is 1,100 miles per hour or 1,770 kilometers per hour. At that speed, it seems like particles would travel far, but they do not. They do not because they bump into other particles and change direction.

Think about watching a bat hitting a baseball. Imagine the bat as one particle in the air. Imagine the baseball as another particle. When the pitcher throws the ball, the ball moves at a very fast speed. If the batter swings the bat at a slow speed, then the ball will bounce off the bat and move away slowly. If the batter swings the bat at a fast speed, then the ball will bounce off the bat faster. If you know about baseball, think about trying to bunt or trying to hit a home run. To make the ball go farther, the batter needs to swing the bat faster. The speed of the bat and the speed of the ball before they hit affect how fast the ball moves after it hit the bat. Particles move a little bit like the bat and ball. The speed of the particles affects how fast they can bounce away from each other. A bat and ball are only two particles. Think of what happens when billions of particles move and bounce off of each other at once.

What Happens to the Speed of Particles When They Are Warm or Cold?

Scientists call temperature the average speed of molecules in a substance. This is true for all substances. When a thermometer measures the air temperature, it measures the average speed of the molecules that make up the air around the thermometer. Here is another way to think about molecules and temperature: When you heat a substance, the particles in that substance move faster. This was true about the ammonia that you saw in class, and it is true about all substances. When you heat a substance, several things happen:

1. The particles move faster. 2. Their energy increases. 3. Faster-moving particles hit into each other harder. 4. Faster-moving particles bounce off of each other harder and move further

apart. 5. As most of the particles that make up the substance move faster, the

temperature increases. What Do Particles Have to do with Odors?When you smell something, you are detecting something traveling through the air that reaches your nose. To smell something, it requires a state of matter with particles that expand beyond their container. Which state of matter does this? The only state of matter capable of this is a gas. Think about the menthol investigation-it was easier to smell the menthol when it was heated and turned to a gas. In fact, the only things we can smell are the gas particles that expand from a substance. Sometimes the gases form from evaporation or sublimation, and sometimes from chemical reactions that create new gases.

Reading #8: How Does Your Nose Work as a Detector? Imagine breathing in and smelling brownies in the oven. How did you detect the odor? As you breathe in through your nose, you force particles in the air to move through your nostrils. They go past the nasal cavity. The nasal cavity is where humans detect odors. In the nasal cavity, odor particles match with receptors called olfactory receptors. Olfactory receptors are like the part of a lock into which a key fits. Specific odor particles fit into a specific receptor like a key fits into only a certain lock. When an odor particle matches with a receptor, a signal travels to the brain through neurons and tells it that a certain odor is in the air.

Why Do I Only Sometimes Smell Odors? One reason why your nose may not detect every odor is because there may not be enough of the specific particles in the air. Another reason is that human noses can only detect certain types of particles. The particles of some materials match with receptors in your nose, but particles of other materials do not match any receptors. You may have guessed that odors that do not match with receptors in your nose are called odorless. You may know that natural gas, by itself, is odorless. It is made of particles that your nose cannot detect. A material with particles your nose can detect is added to help you recognize when natural gas is in the air. The particles that make up the rotten egg odor fit with receptors in your nasal cavity. Those receptors send a signal to your brain that you smell rotten eggs in the air.

What Makes One Odor Smell Different from Another Odor? When different substances have different odors, then either A. the type of atoms they are made of are different, B. the numbers of each type of atom are different, or C. the atoms are connected to each other in different ways.

What Does States of Matter Have to do with Odors?When you smell something, you are detecting something traveling through the air that reaches your nose. To smell something, it requires a state of matter with particles that expand beyond their container. Which state of matter does this? The

only state of matter capable of this is a gas. Think about the menthol investigation-it was easier to smell the menthol when it was heated and turned to a gas. In fact, the only things we can smell are the gas particles that expand from a substance. Sometimes the gases form from evaporation or sublimation, and sometimes from chemical reactions that create new gases.