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".

• There are 3 scales for measuring temperature
  1. Fahrenheit - relative
     • 32F is the normal freezing point temperature of water; 212F is the normal boiling point temperature of water.
  2. Celsius (centigrade) - relative
     • 0C is the normal freezing point temperature of water; 100C is the normal boiling point temperature of water.
  3. 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)

• A form of energy associated with the random motion of the elementary particles in matter.

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

• Specific heat - The amount of heat needed to raise the temperature of one gram of a substance by 1C (or 1 K)
  • SI unit for specific heat is joules per gram^-1 Kelvin^-1 (J/g-K)
  • Calorie - The specific heat of water = 4.184 J/g-K
• Molar heat capacity - The amount of heat required to raise the temperature of one mole of a substance by 1C (or 1 K)
  • SI unit for molar heat capacity is joules per mole^-1 Kelvin^-1 (J/mol-K)
• Btu (British thermal unit) - The amount of heat needed to raise the temperature of 1 lb water by 1F.

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.

• e.g.  The heat that is used to melt ice or to evaporate water is latent heat.

There are two forms of latent heat:

1. Heat of fusion - The heat that must be absorbed to melt a mole of a solid.
   • e.g.  melting ice to liquid water
2. Heat of vaporization - The heat that must be absorbed to boil a mole of a liquid.
   • e.g.  boiling liquid water to steam

Caloric Theory of Heat

• Served as the basis of thermodynamics.
• Is now known to be obsolete
• Based on the following assumptions
  1. Heat is a fluid that flows from hot to cold substances.
  2. Heat has a strong attraction to matter which can hold a lot of heat.
  3. Heat is conserved.
  4. Sensible heat causes an increase in the temperature of an object when it flows into the object.
  5. Latent heat combines with particles in matter (causing substances to melt or boil)
  6. Heat is weightless.
• The only valid part of the caloric theory is that heat is weightless.
• Heat is NOT a fluid, at it is NOT conserved.

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.

Kinetic Theory of Heat

• Divides the universe into two parts:
  1. System - The small portion of the universe in which we are interested.
  2. Surroundings - Everything not included in the system, i.e. the rest of the universe.

• A BOUNDARY separates the system and the surroundings from each other and can be tangible or imaginary.
• Heat is something that is transferred back and forth across boundary between a system and its surroundings
• Heat is NOT conserved.
• The kinetic theory of heat is based upon the last postulate in the kinetic molecular theory which states that the average kinetic energy of a collection of gas particles is dependent only upon the temperature of the gas.  (See Kinetic Molecular Theory notes)

where R is the ideal gas constant (0.0821 L-atm/mol-K) and T is temperature (Kelvin)

• The kinetic theory of heat can be summarized as follows:

Work (w)

• Defined as mechanical energy equal to the product of the force (F) applied to an object and the distance (d) that the object is moved:

• Work, like heat, results from interaction between a system and its surroundings.
• Chemical reactions can do two types of work:
  1. Electrical work - When a reaction is used to drive an electric current through a wire.
     • e.g.  a light bulb
  2. Work of expansion - When a reaction causes a change in the volume of the system.
     • e.g.  a gas pushing up a piston
     • The magnitude of work done when a gas expands is equal to the product of the pressure of the gas and the change in volume of the gas:

Heat and Work

• Thompson's canon-boring experiment showed how work (boring the canon) could produce heat.

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"