Chemistry 2

Heat vs. Temperature

  1. Heat and temperature are not the same thing.
  2. Heat energy is the total kinetic energy of the atoms of a substance.
  3. Temperature is the average kinetic energy of the atoms of a substance.
  4. Test score analogy with points being like heat:
    Test 1 100
    Test 2 50
    Test 3 100
    Test 4 50
    Total points 300
    Average points 75

    Heat is like the total number of points and temperature is like the average score.

  5. Each atom has a certain amount of kinetic energy. This energy fluctuates due to the many collisions with other atoms. However, when two atoms collide transferring kinetic energy from one to the other, no kinetic energy is lost. If the amount of kinetic energy for each atom is added up then you would have a value representing the heat energy of that collection of atoms. It follows that the more atoms which are counted, the greater the heat energy will be.
  6. Temperature is a measure of the average kinetic energy of those atoms. The result of this difference between heat and temperature causes the number of atoms measured to play a major role in understanding how much heat energy an object has at a particular temperature.
  7. For example, if two glasses of water are left out on the table, one completely full and the other exactly half full, they will eventually both come to room temperature, about 21°C. They may have the same temperature, but the full glass has twice the heat energy of the half full glass. Because the full glass has twice as many molecules each carrying some heat energy (or kinetic energy) the full glass has more heat at the same temperature.
  8. The higher the temperature the faster the atoms move.
  9. Large objects can have a kinetic energy and temperature which are distinctly separate things. For example, a baseball sitting still has no kinetic energy, but its atoms are moving, so they have kinetic energy. Because the temperature of a substance is due to the average kinetic energy of its atoms, the ball does have a temperature. Depending on how many atoms it takes to make up the ball, it has a certain amount of heat energy (the total energy of the atoms comprising the ball).
  10. Because temperature is a function of the average kinetic energy of the atoms, the lowest possible temperature would be when the atoms stop moving, therefore having no kinetic energy. Because there is a lowest possible temperature, it would make sense to use a temperature scale that starts at zero. This temperature scale is called the Kelvin temperature scale and zero Kelvin is a special temperature called absolute zero (when all atomic motion is stopped).
  11. An atom, however, can't separate kinetic energy from heat energy. For atoms they are one and the same thing. A bunch of atoms sitting still have no kinetic energy, no heat energy, and would have zero temperature (on the Kelvin temperature scale).
  12. In summary:
    • For an atom Kinetic Energy = Heat Energy
    • For a substance Heat Energy = Total of all the Kinetic Energies of its atoms
    • For a substance Temperature = Average Kinetic energy of its atoms