Heat and the 2 nd Law of Thermodynamics

 Although we learned in the first law that the total amount of energy, including heat, is conserved in an isolated system, it is not possible to use the energy in a system with 100% efficiency.

Heat and the 2 nd Law of Thermodynamics  Heat “Thermal” energy Kinetic energy of atoms and molecules Moves from warmer to cooler object Measured in calories –Amount of heat required to raise 1 gram of room temperature water by 1° Celsius

Heat and the 2 nd Law of Thermodynamics  Heat transfer – Conduction Transfer of heat through collisions of atoms and electrons –Convection Motion of a mass of fluid where warmer atoms are transported from one place to another –Radiation Infrared energy that travels across space until absorbed by an object and converted into kinetic energy of molecules

Heat and the 2 nd Law of Thermodynamics  Temperature –A measurement that reflects how vigorously atoms are moving and colliding in a material –Three temperature scales Fahrenheit Celsius Kelvin –Absolute zero Temperature at which there is no motion of atoms

Heat and the 2 nd Law of Thermodynamics  Comparison of Temperature Scales Water Freezes Water Boils Degrees between freezing and boiling Fahrenheit32° F212° F 180 degrees Celsius0° C100° C 100 degrees Kelvin273° K373° K 100 degrees Absolute zero = 0° K, -273° C and -460° F

Heat and the 2 nd Law of Thermodynamics  Restrictions on the way heat and other energy can be transferred or used –Heat will not flow spontaneously from a cold to hot body –You cannot construct an engine that does nothing but convert heat to useful work –Every isolated system becomes more disordered with time