Matter in Motion运动的物质.doc

MATTER IS THE STUFF AROUND YOU Not very clear, but its true. Anything that takes up space or has a mass of any kind is matter. Everything you can touch is made of matter. If it is made of anything, that anything is matter. Everything you will learn about chemistry will all be based on how matter reacts and combines. Matter has many properties. It can have PHYSICAL properties like different densities, melting points, boiling points, freezing points, color or smells. There are also CHEMICAL properties that define matter. A good example of chemical properties is the way elements combine with each other in reactions. The big thing to remember. Matter can change in two major ways, physically and chemically. If we are to understand how matter is behaving we must understand what is happening at matters most basic level-the smallest particle of matter involved in the change (aka atoms and molecules).Matter in MotionMotion is a common characteristic of large scale samples of matter that are given suitable pushes and pulls (also known as forces). Tennis balls, automobiles, rain drops, popcorn, and dust particles in a ray of sunlight can all be easily visualized in states of motion. But we will learn that even large scale objects seemingly at rest are still in motion! To develop such a view we will examine the behavior of matter more closely-specifically GASES.Recall that there are three main states of matter (with a fourth state that is not too common): SOLIDS, LIQUIDS, GASES, and PLASMAS. These states can also be called “PHASES”. We already know that matter is made of combinations of elements and compounds and (according to Dalton) ultimately-ATOMS!The phase of a substance describes a physical property of matter. The key word here is physical and not chemical because matter will move from one phase to another by physical means. By adding heat or taking heat away, we change the temperature of the substance and its physical state, but the chemical composition and chemical properties of the substance stay the same (usually). Melting is a good example of a change of state. We can proceed from a solid state of matter to a liquid state of matter to a gas. Depending on certain conditions (like temperature and pressure), many different types of matter can exist in all three states. The colder a sample is the more likely it is to be a solid; the hotter it is, the more likely it is a gas. We will discover that PRESSURE as well as temperature can have a strong influence on the behavior of a gas.To understand states of matter and the changes of state more fully, we need to add a new theory to our knowledge. This scientific theory is known as the KINETIC MOLECULAR THEORY (KMT). With any scientific theory, there must be model that can be used to explain it. The scientists model is a simple description or representation of a real system or phenomenon that can be used to study the important aspects and events. By analyzing the structure and behavior of the model, the scientist hopes to develop a clear picture of what is actually going on. In other words, the model provides a test for the original concept or idea. Models can help reveal strengths and weaknesses in any theory.As an example, lets look at a game of football. If a football coach has enough players for two teams, the second team is used as a model for the opposing team in preparation for the next game (also known as “giving the first team a look”). The second team tries to run the same plays the opponents are likely to use in the real game. By running offensive plays against the teams first defense, the model “tests” that defense. The second team is a “model”. It has the same number of players as the opposing team and it runs the same plays. The coach just hopes the opponents arent much better than the second team. Model building and theorizing are common human activities; such activities allow us to simplify and organize all of the data and information that we take in though our senses everyday of our lives. The search for patterns or regularities from our observations often leads to a theory or model that can be used to challenge our current beliefs or better understand the events around us.Kinetic Molecular TheoryAround 1860 (after Dalton), Ludwig Boltzman and James Maxwell (from the Einstein video and electromagnetism fame with Faraday), both in different countries, each proposed a model to explain the properties of gases. Imagine a gas in a balloon-it exhibits some behaviors much different than solids or liquids. Think about air pressure and how it affects our ability to breathe and what might happen when a planes door opens at 35, 000 feet versus sea level. The word kinetic comes from the Greek, “to move”, the study of kinesiology is the study of human motion. Something in motion whether it is a football or a snail has kinetic energy. The KMT makes several predictions about the behaviors of gases which we will find at the end of our discussion about matter. From work done by a “rodent faced” lawyer Amadeo Avogadro, scientists believed that gases were made of very tiny molecules in constant motion. The present kinetic molecular theory is based on a model in which all matter is thought to consist of small particles that are constantly in motion. These particles of matter possess kinetic energy the energy of motion. The amount of kinetic energy that a particle has is determined by how massive the particle is and how fast it is moving. All of the particles in a sample have the same mass, but not the same velocity and not the same kinetic energy. A substance with high energy and fast particles can be measured to have a high temperature as well. But temperature is a measurement of the average kinetic energy in a sample, so some are moving fast while other particles are moving slow.The formula is:KE = mv2; J= kg*m2/v2=Energy of motionwhere m = mass and v = the velocity (like speed) that it is movingIf mass is expressed in kilograms and velocity is expressed in meters per second, then the energy in the particle is called a JOULE (J). The energy in our food is a calorie (cal); 1 cal = 4.18 J. In the simplest picture, the KMT suggests that a solid is like a large pile of vibrating tennis balls. Each molecule is vibrating, but because it is closely surrounded on all sides by other particles, it cant really go anywhere. In a sense it is stuck where it is.SOLID BASICS Solids can be made up of many things. They can have ELEMENTS or compounds inside. They can also be made up of mixtures, or combinations of different elements and compounds. Most of the solids you see are mixtures. Most rocks are mixtures of many elements and compounds. Concrete is a good example of a man-made solid mixture. CHARACTERISTICS OF SOLIDS First lets explain that characteristics are the traits or features that something might have. One characteristic of a solid is that it might be hard. That idea is pretty straight forward. One of the main characteristics of solids is that they hold their own shape. So if you put a solid in a container it wont change its shape. No matter how much you move or slide it around. You can even grind a solid up so that it fills up a container. If you look at the powder under a microscope you will still see little tiny solids that you couldnt change. You know that liquids are different because if you put a liquid into a container it will fill it up as much of the container as it can. In the same way that a solid holds its shape the atoms inside of a solid are not allowed to move around much. This is a physical characteristic of all solids. It happens no matter how small the pieces are. The atoms in liquids and gases move around in all directions. The solid atoms and molecules are trapped in their places. What could be holding those particles in place?SO YOU WANT TO BE A SOLID? Obviously not everything is a solid. If you look around youll see solids, liquids, and especially gases (remember the air around you). Sometimes liquids feel a physical need to become a solid. Then look out! Phase changes are about to happen. Scientists use something called a FREEZING POINT to measure when a liquid turns into a solid. There are physical effects that can change the freezing point. Pressure is one of those effects. When the pressure surrounding a substance goes up the freezing point also goes up. That means its easier to freeze the substance at higher pressures. When it gets colder, most solids shrink in size. There are a few which expand but most shrink. CRYSTALS If a solid is made up of pure elements or compounds something special happens. It can freeze into a very specific structure. This structure is called a CRYSTAL LATTICE. A crystal lattice is a very exact organization of atoms which creates a specific place for every molecule or atom in the solid. It is very neat and very compact. A great example of a crystal lattice is a diamond.Now if we add some heat energy to the solid, the temperature of the solid increases. As the energy increases the, particle movement (vibrations) increase. They start “bouncing” into one another in a random fashion, like popcorn kernels in a popcorn popper. Finally, some of the faster-moving particles knock others out of the way and then move about more freely. Our once organized structure of particles is now disordered and more random.But what has happened to our nice orderly arrangement of particles when we have reached this point? The regular arrangement has started to melt or liquefy. This can be described as liquids developing “holes”. These holes affect the density of the liquid by increasing the volume (amount of space) of the substance. The density of the liquid is less than the corresponding solid (water is a curious exception to this). Most substances behave like iron when it melts. Its density as a solid is 7.86 g/mL and as a liquid it has a density of 6.88 g/mL. LIQUID BASICS By now you know what a solid is. If you wave your arms around you can find a gas. But what about liquids? Not that we suggest it but you know youve got some spit. Thats a liquid. What about your blood? Thats a liquid too. The main thing is to figure out what makes those things liquids. Liquids are an in-between phase of matter. They are right between solids and gases. One characteristic of a liquid is that it fills the shape of any container. So you pour some water in a cup. It fills up the bottom of the cup first and then fills the rest. It also takes the shape of the inside of the cup. It starts filling at the bottom because of GRAVITY. When it is in that cup it also has a flat surface. Thats because of gravity too. One other characteristic of liquids is that they are very hard to COMPRESS. When you compress something you take a certain amount and force it in a smaller space. Solids are tough to compress too, but gases are easy. When you compress something you squeeze it so the atoms in the substance are closer together. When pressure goes up substances are compressed. Liquids already have their atoms close together so its hard to push them even closer. SO YOU WANT TO BE A LIQUID? If you want to be a liquid you could start out as two different things. You could be a solid or you could be a gas. Each of them has a different way of becoming a liquid. Lets say youre a solid. Thats you-a pure cube of ice sitting on a counter. All you do is dream of becoming liquid water. What you need is some ENERGY. Atoms in a liquid have more energy than the atoms in a solid. The easiest energy around is probably heat. There is a magic temperature for every substance called the MELTING POINT. When a solid reaches the temperature of its melting point, it can become a liquid. For water the temperature has to be a little over zero degrees Celsius. If you were salt, sugar or wood your melting point would be higher than water. So solids need more energy. The reverse is true if you are a gas. You need to lose some energy from your very excited gas atoms. The easy answer is to lower the surrounding temperature. When the temperature drops, energy will be sucked out of your gas atoms. When you get to the CONDENSATION POINT, thats the temperature when you become a liquid. If you were the steam of a boiling pot of water and you hit the wall, the wall would be so cool that you would quickly become a liquid. Now lets summarize.A model of matter which led to the kinetic molecular theory represents solids and liquids as being made of constantly moving particles-particles such as atoms and molecules. In a solid the particles are closely packed-usually ordered and organized. In a liquid the particles are less tightly packed and less neatly arranged. The kinetic energy of the particles in a liquid is greater than the kinetic energy of particles in the solid form of the same substance (this is why the temperatures are different). Before finding your gas, try some questions on for size. What happens to the particles in a liquid as it cools? Do all the particles in a liquid move with the exact same velocity? What might happen if you dropped some “cold” (slow moving) particles into a bucket of “hot” (fast moving) particles? Why might different substances have different melting points? Does the temperature of a substance stay constant during melting or boiling?LOOKING FOR GAS You want to identify a gas? Maybe youre standing next to your friend and you hear him make a little farting noise. Not here buddy. Were not talking about that kind of gas. Flatus is not funny. Maybe it is, but it has no place here. Not yet anyway. Gas is everywhere. There is something called the ATMOSPHERE. Thats a big layer of gas that surrounds the Earth. Gases are random groups of atoms. There are solids where atoms and molecules are really compact. Liquids have them a little more spread out. But gases are really spread out and the atoms and molecules are full of ENERGY, bouncing around constantly. In fact the word “gas”, comes from the Greek word “chaos” which means “without order”. Think about the gases given off in the chemical reactions we have done, they are pretty difficult to collect and measure. One of the physical characteristics is that a gas can fill a container of any size or shape. Think about a balloon for a minute. No matter what shape you make the balloon it will be completely filled with the gas. The atoms and molecules are spread equally throughout the entire balloon. Liquids can only fill the bottom of the container while gases can fill it entirely. BEING A GAS I bet that you want to be a gas right now. Trust Peter Griffin. Its easier to make gas than to become one. First you need some beans, ah I digress. Actually you need energy to become a gas. The atoms in a gas have more energy than the atoms in solids and liquids. The easiest way to think of energy is to think of temperature. When you increase the temperature of a system you are pouring energy into that system. Extending the KMT, what happens if we continue to add heat energy to our liquid sample? The theory suggests that the particles move faster and faster and more “holes” appear in the liquid, and the system becomes less orderly; volume is increased. Finally, some of the fastest moving particles have enough energy and velocity to break away completely from the others and escape into space. The substance is boiling. Adding energy eventually puts all of the particles into the gaseous state. Gases are the most random and disordered state of matter that we would run into here on earth.When you want to be a gas you usually start out as a liquid. If you add energy to a liquid you might hear the term VAPOR. Vapor and gas mean the same thing. The word vapor is used to describe gases that are usually found as liquids (like water). A compound like CO2 is usually a gas, so it described that way. But water (H20) is usually found as a liquid at room temperature. So when it becomes a gas scientists use the term vapor. EVAPORATION Sometimes a liquid can be sitting there and its molecules will become a gas. Thats called EVAPORATION. You might be wondering how that can happen when the temperature is low. It turns out that all liquids can evaporate at room temperature and pressure. Evaporation is when there are atoms or molecules escaping from the liquid and turning into a vapor. You see. Not all of the molecules in a liquid actually have the same energy. The energy you can measure is really an AVERAGE of all the molecules. There are always a few molecules with a lot of energy and some with barely any energy at all. It is those with a lot of energy that build up enough power to become a gas and leave the liquid. When it leaves it has evaporated.KMT and GasesThere are three “assumptions” about behaviors of gas particles (from Glencoe, 2002). The theory attempts to explain the behavior of gases, like their low density, compressibility, diffusion, and effusion. Particle size Gases are small particles that are separated by empty space. The volume of a gas is compared to the volume of the empty space. Because the particles are far apart, gases do not attract or repel one another. Particle motion Gas particles are constantly moving in a random fashion. They will move in a straight line unless a collision with another object or particle. Gas particles collide in an “elastic” fashion where kinetic energy is transferred but not lost. Particle energy As mentioned in the beginning of this reading, the kinetic energy of a gas particle is dependent on the mass of the particle and the velocity of the particle. All of the particles in a sample of gas like hydrogen all have the same mass, but not all of the particles in a gas have the same velocity.Temperatur