Gas constant

From Freepedia

Values of R
8.314472 J · K-1 · mol-1
0.08205746 L · atm · K-1 · mol-1
8.2057459 x 10-5 m³ · atm · K-1 · mol-1
8.314472 L · kPa · K-1 · mol-1
62.3637 L · mmHg · K-1 · mol-1
62.3637 L · Torr · K-1 · mol-1
83.14472 L · mbar · K-1 · mol-1
1.987 cal · K-1 · mol-1
10.7316 ft³ · psi · °R-1 · lb · mol-1

The gas constant (also known as the universal or ideal gas constant, usually denoted by symbol R) is a physical constant used in equations of state to relate various groups of state functions to one another.

The gas constant occurs in the simplest equation of state, the ideal gas equation, as follows:

<math>

p = {RT\over{\tilde{V}}} </math> where p is the pressure of an ideal gas, T is its temperature, and <math>\tilde{V}</math> is its molar volume. R also appears in the Nernst equation as well as in the Lorentz-Lorenz formula. P = power but p = pressure.

Its value is:

R = 8.314472[15] J · K^-1 · mol^-1

The two digits in brackets signify the uncertainty (standard deviation) in the last two digits of the value.

The gas constant is conversion factor between gas units. It tells how many joule per kelvin make a mol.

The Boltzmann constant k_B is defined as a ratio of molar gas constant and the Avogadro's number (Avogadro's number is approximately 6.022 × 10²³ particles/mole):

<math>k_B = \frac{R}{N_A}</math>

The Boltzmann constant is conversion factor between gas units. It tells how many joule per kelvin make a molecule.

With it we can write the ideal gas equation:

<math>\qquad PV=Nk_BT</math>

with N = nN_A is the actual number of molecules.

External links

• gas constant CODATA value at NIST