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Multiplying by the number of particles N yields the change in entropy of the entire system from the unmixed case in which all of the p i were either 1 or 0. We again obtain the entropy of mixing on multiplying by the Boltzmann constant k B {\displaystyle k_{\text{B}}} .
In the case of an ideal gas, the heat capacity is constant and the ideal gas law PV = nRT gives that α V V = V/T = nR/p, with n the number of moles and R the molar ideal-gas constant. So, the molar entropy of an ideal gas is given by (,) = (,) + . In this expression C P now is the molar heat capacity. The entropy of inhomogeneous ...
The gas constant occurs in the ideal gas law: = = where P is the absolute pressure, V is the volume of gas, n is the amount of substance, m is the mass, and T is the thermodynamic temperature. R specific is the mass-specific gas constant. The gas constant is expressed in the same unit as molar heat.
For the expansion (or compression) of an ideal gas from an initial volume and pressure to a final volume and pressure at any constant temperature, the change in entropy is given by: = = Here is the amount of gas (in moles) and is the ideal gas constant.
The Van 't Hoff equation relates the change in the equilibrium constant, K eq, of a chemical reaction to the change in temperature, T, given the standard enthalpy change, Δ r H ⊖, for the process. The subscript r {\displaystyle r} means "reaction" and the superscript ⊖ {\displaystyle \ominus } means "standard".
The internal energy of any gas (ideal or not) may be written as a function of the three extensive properties , , (entropy, volume, number of moles). In case of the ideal gas it is in the following way [15] (,,) = +, where is an arbitrary positive constant and where is the universal gas constant.
Another equivalent result, using the fact that =, where n is the number of moles in the gas and R is the universal gas constant, is: =, which is known as the ideal gas law. If three of the six equations are known, it may be possible to derive the remaining three using the same method.
The Sackur–Tetrode constant, written S 0 /R, is equal to S/k B N evaluated at a temperature of T = 1 kelvin, at standard pressure (100 kPa or 101.325 kPa, to be specified), for one mole of an ideal gas composed of particles of mass equal to the atomic mass constant (m u = 1.660 539 068 92 (52) × 10 −27 kg [5]).