**The Ideal Gas Law**

To derive the ideal gas law, we can extend the argument we used to derive the
combined gas law. According to Boyle's law V = k_{1}/P and according to
Charles's law V = k_{2}T, while Avogadro's law leads to V = k_{3}n, where
n is the number of moles of gas. If we combine the three equations, we obtain the
equation V = k'T/P. For one mole of gas the constant k' is called **the molar
gas constant **and is given the symbol **R.**

According to Avogadro's law, the molar volume at a specific value of T and P is a
constant, independent of the nature of the gas. For n moles of gas the **ideal
gas law **is represented by the equation **PV = nRT.**

The value of the **molar gas constant, R, **depends on the units used
for pressure and volume. In all cases T is kelvins. Values of R in various
units are shown in the table below.

**Value of R**

0.082058 L · atm/(K · mol)

8.3145 J/(K · mol)

8.3145 kg · m^{2}/(s^{2} · K · mol)

8.3145 kPa · dm^{3}/(K · mol)

1.9872 cal/(K · mol)