Thermodynamics :  Temperature, Heat, and Work

Thermodynamics - The study of the relationship between heat, work, and other forms of energy.

Thermochemistry - A branch of thermodynamics which focuses on the study of heat given off or absorbed in a chemical reaction.

Temperature - An intensive property of matter; a quantitative measurement of the degree to which an object is either "hot" or "cold".

  1. There are 3 scales for measuring temperature
    • Fahrenheit - relative
      • 32F is the normal freezing point temperature of water; 212F is the normal boiling point temperature of water.
    • Celsius (centigrade) - relative
      • 0C is the normal freezing point temperature of water; 100C is the normal boiling point temperature of water.
    • Kelvin - absolute
      • 0 K is the temperature at which the volume and pressure of an ideal gas extrapolate to zero.

Conversion Factors for Temperature

Heat (q)

Heat capacity - The amount of heat needed to raise the temperature of a defined amount of a pure substance by one degree.

NOTE:  The specific heat of water (4.184 J/g-K) is very large relative to other substances.  The oceans (which cover over 70% of the earth) act as a giant "heat sink," moderating drastic changes in temperature.  Our body temperatures are also controlled by water and its high specific heat.  Perspiration is a form of evaporative cooling which keeps our body temperatures from getting too high.

Latent Heat versus Sensible Heat

Sensible heat - Heat that can be detected by a change in the temperature of a system.

Latent heat - Heat that cannot be detected because there is no change in temperature of the system.

There are two forms of latent heat:




Caloric Theory of Heat

1798 - Sir Benjamin Thompson (Count Rumford)

  • Canon-boring experiment showed that friction was an inexhaustible source of heat.  He concluded that heat, therefore, was not conserved. 
  • This experiment served as a starting point for the development of a new theory, the kinetic theory of heat. 

When heat enters a system, it causes an increase in the speed
at which the particles in the system move.



Work (w)

Heat and Work

1838 - James Prescott Joule

  • Did several experiments measuring how much heat could be produced from a given amount of heat. 
  • In his most well-known experiment, Joule used falling weights connected to a rope wrapped around rotating paddles.  The paddles were placed in either water, mercury, or oil and he measured the change in temperature of these liquids when the weights were dropped. 
  • One joule is by definition the work done when a force of one newton (N) is used to move an object one meter (m): 

Next:  "First Law of Thermodynamics"