Exercise 4 | Properties of Gases

Ideal-gas equation:

PV = nRT    and    n = N / N_A

⇒ PV = $\frac{\mathrm{NRT}}{{\mathrm{N}}_{\mathrm{A}}}$

⇒ N = $\frac{{\mathrm{PVN}}_{\mathrm{A}}}{\mathrm{RT}}$

P = pressure in Pa ⇒ 1.0 x 10^-5 torr = 1.3 x 10^-3 Pa

V = volume in m³ ⇒ 1.0 L = 1.0 dm³ = 1.0 x 10^-3 m³

N_A = Avogadro’s number = 6.022 x 10²³

R = ideal gas constant = 8.314 m³.Pa.K^-1.mol^-1

T = temperature ⇒ 25.0°C = 298 K

N = $\frac{1.3 \times {10}^{-3} \times 1.0 \times {10}^{-3} \times 6.022 \times {10}^{23}}{8.314 \times 298}$ = 3.2 x 10¹⁴ molecules