Intensity and Capacity Factors of Energy
| Energy Form | Intensity or Intensity Property | Capacity or Extensive Property | Commonly used Energy Unit (Work) |
| Heat (Thermal) | Temperature (degree) | Entropy Change (cal/deg) | Calories |
| Expansion | Pressure (dynes/cm2) | Volume Change (cm3) | ergs |
| Surface | Surface Tension (dynes/cm) | Area Change (cm2) | ergs |
| Chemical | Chemical Potential (cal/mole) | Number of Moles | Calories |
As an example consider the mechanical work done by a gas on its surroundings W = PdV
Thermodynamic can also applies to the surface of a liquid.
As an example Surface Free Energy = Surface Tension times the change
in surface area. OR Fs = Gamma X dA
THE FIRST LAW OF THERMODYNAMICS
The First Law of Thermodynamics states that energy can neither be created nor destroyed.
Energy can change forms or move from one body to another but the total energy of the system cannot change. Einstein developed a relationship between matter and energy which simple put equated the two. The energy content of even a small amount of matter if converted to energy is so large compared to the energy of pharmaceutical systems that E = MC2 is only included her for completeness. The first law can be written mathematically as:
Other words that must be defined in thermodynamic terms include
Closed vs Open System - A closed system is one that does not exchange matter with the outside while an open system does exchange matter with the outside.
Isothermal Process - is one which is carried out without a change in temperature
Adiabatic Process - is one that is carried out without a change in the heat content of the system.
Boiling water is an isothermal process as the temperature of the water
stays at 1000C even though you add heat to the system. The extra
heat escapes the system as steam. A reaction carried out inside a
Deware flask is adiabatic as no heat can escape the flask.
The equation changes in an adiabatic system to dE = -W since q = 0.
The simplest system to use to understand these process is the expansion of a gas.
As you heat a gas in a container with at least one movable side, like a piston, the heat will add energy to the gas which will expand against the pressure pushing down on the piston. The movement of the piston does work. W = PdV
In a steam locomotor we actually convert water to steam. The volume is greatly expanded as a result of this process and the expanding water vapor moves the piston. If we perform this change of state at the boiling point of water the heat absorbed by the water is called the heat of vaporization (Hv) and is about 9270 calories/mole. The work of expansion against atmospheric pressure is a function of the change of volume when one mole of liquid water 18 ml expands to 30.6 liters of water vapor.
How did I know the volume of one mole of water??
I used the ideal gas law to calculate the volume of one mole of water
vapor at 1000C.
V = n RT/P where n = 1, R=0.082 liter atm/ mole degree and T is in degrees
Kelvin or 3730
Work is the product of the pressure times the change in volume.
W = 1 atm X (30.6 - .018) = 30.6 liter atm/mole = 741 calories
E = 9270 calories - 741 calories = 8979 cal/mole
In class we will also discuss heat content and define Enthalpy in mathematical terms.
Heat Capacity is the amount of heat that must be absorbed by one mole
of a substance to raise the temperature one degree. Often written
as C = q/dT