VIEWS: 3 PAGES: 3 POSTED ON: 1/7/2012
Heat and 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. 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. Gabriel Fahrenheit • In the briefest terms, Fahrenheit took a glass tube and graduated it…made marks, 1,2,3 etc. He used water as the standard. • 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. Anders Celsius • When Anders Celsius investigated the subject of temperature he did something a little differently. 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. Lord Kelvin • 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. CALORIES • In our society we count calories. We measure the number of calories in a candy bar. We have weight watchers which watches calorie intake. • So what are calories?? • It 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 “burn ed” off by DOING WORK…that is by transferring the energy of your body to the world around you. • And that will heat up the universe and thus speed us toward “heat death” or maximum entropy. QUANTIFICATION • Heat 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 • F - 32 / 1.8 = C • K = C + 273 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. • So what happens to a solid when the temperature goes up…that means heat is going INTO the system. Energy is going into the system. The molecules start to move faster and try to get farther apart. Those forces that held the molecules in place as a solid aren’t quite strong enough to hold the atoms and molecules in place and the molecules start to separates and the forces are weaker, more like slinky springs holding the atoms together. So the molecules slide around each other…a liquid. The molecules “flow” past each other. • The 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).
Pages to are hidden for
"Heat and temperature"Please download to view full document