Search results
Results from the WOW.Com Content Network
The internal energy depends only on the internal state of the system and not on the particular choice from many possible processes by which energy may pass into or out of the system. It is a state variable, a thermodynamic potential, and an extensive property. [5] Thermodynamics defines internal energy macroscopically, for the body as a whole.
The other equation of state of an ideal gas must express Joule's second law, that the internal energy of a fixed mass of ideal gas is a function only of its temperature, with = (,). For the present purposes it is convenient to postulate an exemplary version of this law by writing:
Hence, all the energy possessed by the gas is the kinetic energy of the molecules, or atoms, of the gas. = This corresponds to the kinetic energy of n moles of a monoatomic gas having 3 degrees of freedom; x, y, z. The table here below gives this relationship for different amounts of a monoatomic gas.
If the amount of substance in moles can be determined, then each of these thermodynamic properties may be expressed on a molar basis, and their name may be qualified with the adjective molar, yielding terms such as molar volume, molar internal energy, molar enthalpy, and molar entropy. The symbol for molar quantities may be indicated by adding ...
If the calorically perfect gas approximation is used, then the ideal gas law may also be expressed as follows = where is the number density of the gas (number of atoms/molecules per unit volume), = / is the (constant) adiabatic index (ratio of specific heats), = is the internal energy per unit mass (the "specific internal energy"), is the ...
Here is the number of moles of gas and is the molar ideal gas constant. Because the internal energy does not change and the internal energy of an ideal gas is solely a function of temperature, the temperature of the gas does not change; therefore =.
For example, terrestrial air is primarily made up of diatomic gases (around 78% nitrogen, N 2, and 21% oxygen, O 2), and at standard conditions it can be considered to be an ideal gas. The above value of 1.4 is highly consistent with the measured adiabatic indices for dry air within a temperature range of 0–200 °C, exhibiting a deviation of ...
The properties of molar internal energy and entropy —defined by the first and second laws of thermodynamics, hence all thermodynamic properties of a simple compressible substance—can be specified, up to a constant of integration, by two measurable functions: a mechanical equation of state = (,) , and a constant volume specific heat