Heat and Temperature 10-2 and 10-3

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 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.

Anders Celsius When 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.

Lord Kelvin Kelvin 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.

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. K=C+273 C= K-273 C= (F-32) x5/9 F= (C x 9/5) +32

Temperature Conversion Practice 1)250 Kelvin to Celsius 2)339 Kelvin to Celsius 3)17 Celsius to Kelvin 4)55 Celsius to Kelvin 5)89.5 Fahrenheit to Celsius 6)383 Kelvin to Fahrenheit

Phase Change Diagram Increasing Temperature Melting Freezing Sublimation Deposition Vaporizing Condensing

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. Conduction Convection Radiation

Conduction 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.

Convection 2. The second way that Q travels from one place to another is via convection. Heat travels through fluids this way Let 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.

Radiation 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.

Lets Review  Heat is the transfer of thermal energy between substances that are at different temperatures.  The energy is always transferred from the warmer substance to the cooler substance.  Heat is the result of molecules vibrating quickly. Therefore heat is moving energy.  The more KE the particles have the higher the temperature.  As temperature increases, so does thermal energy (because the kinetic energy of the particles increased).  Heat is transferred through convection, conduction and radiation.