Ideal gas law

Essential knowledge 9.2.A.2 defines an ideal gas as one whose pressure, volume, amount and temperature can be modeled by that equation. The two halves are the same statement with the gas counted two ways:

• $n$ is the number of moles, paired with the universal gas constant $R = 8.31\ \mathrm{J/(mol \cdot K)}$.
• $N$ is the number of atoms, paired with Boltzmann's constant $k_B = 1.38 \times 10^{-23}\ \mathrm{J/K}$.

They are linked by $N = n N_0$, with Avogadro's number $N_0 = 6.02 \times 10^{23}\ \mathrm{mol^{-1}}$. All three values are printed on the sheet. Use whichever form the question counts in.

Kelvin is not a preference. Pressure is proportional to $T$ at fixed volume, so $T = 0$ must be where pressure vanishes, and Celsius puts its zero nowhere near that point. Pressure belongs in pascals and volume in cubic meters for a related reason: $R$ is quoted in joules, and $\mathrm{Pa} \cdot \mathrm{m^3} = \mathrm{J}$. Leaving a volume in liters costs a factor of a thousand.

What makes a gas ideal is spelled out at 9.2.A.1: the instantaneous velocities of the atoms are random, the atomic volumes are negligible against the total volume, the collisions are elastic, and the only appreciable forces are those during collisions.

The law says nothing about which gas it is: equal numbers of moles of helium and of nitrogen at the same pressure and temperature occupy equal volumes.