Heat and the 2nd Law of Thermodynamics

Created by Dr Adele Register

Heat and the 2nd 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.

Potential Energy






“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 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


A measurement that reflects how vigorously atoms are moving and colliding in a material

Three temperature scales


Absolute zero - Temperature at which there is no motion of atoms


A comparison of temperature scales

  Water Freezes Water Boils Degrees between
freezing and boiling
Farenheit 32° F 212° F 180 degrees
Celsius 0° C 100° C 100 degrees
Kelvin 273° K 373° K 100 degrees

Heat and the 2nd 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