Unit 2 Heat and temperature
What does this have to do with energy transfer or heat flow? - Collisions of particles transfer energy, in effect creating heat transfer by conduction. Particles often collide with each other, when this happens energy is transferred from the faster (hotter) moving particle to the slower (cooler) moving particle. This makes the slower moving particles increase in speed.
When molecules in a substance are made to move faster, they get warmer When molecules in a substance are made to move faster, they get warmer. The warmer an object gets, the more kinetic energy and thermal energy it contains. Kinetic energy – energy of motion Thermal energy – total energy of the atoms and molecules
What does all of this have to do with temperature? -Temperature is the measurement of the average internal kinetic energy of the material or object. When a material reaches the temperature at which a change in state occurs, the temperature will remain the same until all the energy is used to change the state.
How high can something’s temperature go? -In principle, temperature has no upper limit. However, there is a limit to how cold something can get, it is absolute zero. At this point all particle movement has stopped.
What is heat? What is cold? -Heat is the movement, or transfer of thermal energy. -Cold is the lack of thermal energy. The direction of thermal energy flow is always from warmer to colder. Ex. Hand touches a hot stove – hand gets burned Ex. Hand touches ice – ice starts to melt.
Is all of the heat transferred, or is some destroyed? -It can’t be destroyed; it is transferred without a net loss or net gain. The Law of conservation of energy states that energy can not be created or destroyed, it can only be changed from one form to another.
We apply the above law to thermal systems to get the First law of thermodynamics: -Whenever heat flows into or out of a system, the gain or of loss thermal energy equals the amount of heat transferred.
The Second law of thermodynamics restates what we’ve learned about the direction of heat flow. -Heat never spontaneously flows from a cold substance to a hot substance.
The Third law of thermodynamics deals with absolute zero. -No system can reach absolute zero.
Heat Transfer & Change of Phase Why does a silver spoon in left in very hot soup get hot too? -Thermal energy is transferred from the hot end of the spoon through the entire length, it’s called conduction.
Conduction is the transfer of heat energy by collisions between particles in a substance (especially a solid). Electrons in atoms collide with each other inside the object being heated. Good conductors of heat are metals with loose electrons – silver, copper, iron, etc. Poor conductors are called insulators. These don’t have loose electrons – wool, wood, paper, styrofoam, etc.
Do liquids and gases transfer heat by conduction? -Liquids and gases transfer heat mainly by convection. Convection is the transfer of heat by motion of a fluid, or by currents.
When does heat transfer occur? -Heat Transfer occurs whenever matter changes phases. When energy is added and absorbed, the change of phase will move in the following direction: solid > liquid > gas When energy is released, the change of phase will move in the following direction: gas > liquid > solid