3 Heat vs. Temperature Heat is energy- it can do work. Temperature is a man-made, arbitrary scale indicating which direction heat is flowing…is heat going into the system, temperature rising or is heat leaving the system, temperature declining.Heat is measured with an instrument called a calorimeter.Heat is NOT measured with a thermometer.Temperature is measured with a thermometer.Heat is measured in Joules.Temperature is measured in degrees.
4 There are 3 thermometers which measure temperature. Recall that a thermometer is a man made scale simply indicating the direction of heat flow. It is also a relative measure of the motion of molecules in the system.If the molecules are moving fast with lots of KE then the temperature is high because a lot of heat is in the system.If the temperature is low then we may assume there’s not as much heat in the system and we can expect the molecules to be moving slower with less KE…generally less energy in the system.
5 Gabriel Fahrenheit and Anders Celsius In the briefest terms, Fahrenheit took a glass tube and graduated it…made marks, 1,2,3 etc. He used water as the standard. We often do use water as our standard for things, it is cheap and plentiful and easy to get.He froze some water and the mercury in the tube dropped to the mark he had made…32 degrees. When water boiled the mercury in the tube rose to 212 degrees.That is the thermometric scale we use in the USA.
6 Anders CelsiusWhen Celsius investigated the subject of temperature he did something a little differently. He did not mark off the glass tube. He simply put it into frozen water and where the mercury landed he called that 0 degrees. When water was boiling and the mercury rose and leveled off he called that 100 degrees.This is the one use most around the world.Although in science we use a third thermometer when dealing with extreme temperatures.
7 Lord KelvinKelvin was interested in a more philosophical approach to the behavior of matter at different temperatures. He wondered, for example, what would happen if there was a condition of NO HEAT. At “absolute” zero what would the conditions be?At zero Kelvin, at absolute zero, all motion would cease since temperature is an indirect measure of the motion of molecules. So if there was no heat there would be no motion and thus no temperature. But a condition of absolute zero cannot exist since there is no absolute NO motion. Everything moves relative to SOME frame of reference. So EVERYTHING has SOME temperature.Atoms vibrate. Electrons revolve around the nucleus of every atom. EVERYTHING MOVES RELATIVE TO SOMETHING.
8 QUANTIFICATIONHeat and temperature can be measured and quantified through a series of equations.There are 3 thermometers, 3 temperature scales. We can convert from one thermometer to another via these equations.°F = (1.8 x ° C) + 32° C = ° F - 32 / 1.8K = ° C + 273
9 CALORIESIn our society we count calories. We measure the number of calories in a candy bar.So what are calories?? Energy needed to raise 1 gram of water 1°CIt turns out that a long time ago people thought heat was a fluid, made of atoms, like air . They thought it had weight and mass and was a “Thing”. They called this substance “caloric”But, it turns out that heat is NOT a thing, not made of atoms, not a substance at all. But the name stuck…heat was caloric.So when we talk about calories we are talking about energy today and the amount of energy we are taking in to our body. We must USE that energy we have taken in OR our bodies will convert it to the storage form of energy…FAT. Fat is simply the body’s way of saying…don’t want to use that energy now? OK. I will save it for you for later.Sooner or later that must be released into the universe…that energy must be “burned” off by DOING WORK…that is by transferring the energy of your body to the world around you.1000 calories = 1 Calorie, also known as a kcal.
10 Quantifying heat as the temperature changes and the heat causes a phase change. There are 3 common state of matter, solids liquids and gases.Whether the substance is in its solid, liquid or gaseous state depends on the TEMPERATURE.Consider water. As ice the molecules are moving very slowly, they have little energy and so electric attractive forces between molecules is strong enough to hold the molecules in place…a solid. A solid has a definite shape, holds that shape at that temperature and it has a definite measurable volume at a a given temperature so that if we know the mass we may calculate the density of the sample.
11 Phase ChangeThe liquid state has more energy than the solid state of a given substance. Energy in the form of heat was added to the system. Now what happens when even more energy is added?We know more energy is being added into the system because the temperature is rising. Eventually the temperature will be high enough that the forces that held the atoms and molecules together as a solid and even as a liquid aren’t strong enough to hold the atoms and molecules together so that they fly apart and go off independently, fly anywhere they like. That is a gas (vapor).
12 So the equations are??? Q = m c ΔT Now what does that mean? Suppose we want to know HOW MUCH HEAT is needed to change the temperature of a substance…this is the equation we use.Q= heat. The unit of heat will be either the SI unit of heat energy called JOULES or it may be measured in Calories as well, the older unit of heat.M = Mass. The amount of heat needed to change the temperature of a certain amount of a substance depends in part on HOW MUCH of the substance you have. Obviously you must do much more work to change the temperature of a ton of iron than it will take to change the temperature of 1 ounce of iron.“c”= is called the “specific heat” of a substance. It turns out that every substance has a characteristic specific heat. We can identify an unknown substance IF we know its specific heat. So when I wish to find out how much heat is needed to change the temperature of a substance it helps to know the mass and the identity of the substance.The third piece of info needed is the amount of temperature change.So it will take more energy, more work, more heat to change the temperature by 50 degrees than to change the temperature by only 10 degrees.Q = mc Δ T If I know the mass and the identity of the substance and the amount by which we wish to change the temperature of a substance then we can calculate the amount of work, energy, heat needed to make the change.
14 Heat can travel but Temperature does not. Temperature can change as heat is added or removed. But temperature is a man made scale.Heat is pure energy. It does work. It can cause masses to move.Heat can also be transferred. Recall that work is the transfer of energy. So heat can transfer from one place to another.Heat can travel from one place to another by 3 ways.1. Heat can travel by CONDUCTION. One object can cause cooler objects to heat up. Heat ALWAYS and ONLY travels from HOT to COLD. So via conduction, a hotter object can transfer the energy to a cooler object.It happens by contact. One object touches another and the energy of the hotter causes the molecules of the cooler to begin to move faster, that is they have more energy and thus the temperature goes up. Consider a metal spoon in a pan of hot soup. The handle would eventually get hot even though only the bowl of the spoon is in the soup so the atoms of hotter collide with atoms of cooler and transfer their energy.Conduction is the way heat travels through solids.
16 Convection2. The second way that Q travels from one place to another is via convection. Heat travels through fluids this wayLet us define a fluid…A fluid is anything that flows. Liquids flow. But so do gases…air masses flow in currents, air flows.When liquids and gases are heated, gain more energy then they become less dense. The molecules move faster and farther apart. Same mass in larger volume. As a result of less density hot liquids and gases rise.Removing energy from liquids and gases cools substances. The atoms and molecules have less energy, move slower, cannot escape gravity easily or for as long and so they tend to fall together and sink.“Fall together” means the molecules and atoms get closer to one another. That is the sample becomes more dense. The mass is the same but the volume is smaller. Because the molecules are more dense and because of that it sinks. Colder gases or liquids sink.
17 Radiation3. Radiation is the way heat can travel through a vacuum, through empty space.Heat travels through nothing on something called an electromagnetic wave.This is how heat reaches us from the sun.We will study more about EMR as we study light later on down the line.Radiation, waves, shouldn’t be confused with harmful radiation, that is waves of energy produced when the nucleus of an atom falls apart and radioactivity is released.This is just heat moving through space in something called an electromagnetic wave.Matter can react to EMR in two ways. The heat waves can be absorbed. The energy is taken in , the molecules start to move faster and the temperature goes up.OR….Matter can reflect the heat waves. That is the object does not absorb the energy but simply allows it to bounce back like throwing a ball against a wall.
22 Phase Change DiagramThe phase change diagram is just a visual way to describe and calculate all the heat needed to change the temperature of a sample through the 3 phases of matter, solid to liquid to gas.
23 Heat EquationsYou need two equations. Q=mCΔT as we have just discussed and Q = m ΔHv.Or…Q= m ΔHf.Heat = mass times the heat of vaporization and mass times the heat of fusion.It turns out the ΔHv, and the ΔHf are both characteristic of a substance…we could use to identify an unknown if we knew that value.Heat of vaporization, ΔHv, is the amount of heat needed to boil / condense 1 gram of your sample.Heat of fusion, ΔHf, is the amount of heat needed to freeze/melt 1 gram of your sample.
24 Melt-Freeze Boil-Condense It turns out that the temperature at which a solid melts to a liquid, whether ice or iron,Is characteristic of the material. Aluminum melts at 660 CTin melts at 232CWater(ice) at 0CIron melts at 1535 CIt turns out that the temperature at which water freezes to a solid is also 0CMolten iron will freeze at 1535 CLiquid Tin will freeze at 232 CEtc. etc. etc.What do you notice about the temp. at which a substance melts or freezesIt is the same!
25 (hit green Run Now! Button.) (hit green Run Now! Button.)Gas law: P V= n R T