To calculate the surface density of adsorbed molecules, we can use the Langmuir adsorption isotherm equation:
Γ = (P * A) / (k * T)
where:
Γ is the surface density of adsorbed molecules in mol/m²,
P is the gas pressure in Pa,
A is the binding energy per molecule in J,
k is the Boltzmann constant (1.38 x 10^-23 J/K),
T is the temperature in Kelvin.
First, let's convert the binding energy from eV to J:
1 eV = 1.602 x 10^-19 J
So, the binding energy is 0.02 eV * 1.602 x 10^-19 J/eV = 3.204 x 10^-21 J.
Now, let's calculate the surface density at 12 K:
Γ₁ = (103 Pa * 3.204 x 10^-21 J) / (1.38 x 10^-23 J/K * 12 K)
Γ₁ ≈ 1.87 x 10^5 mol/m²
Next, let's calculate the surface density at 68 K:
Γ₂ = (103 Pa * 3.204 x 10^-21 J) / (1.38 x 10^-23 J/K * 68 K)
Γ₂ ≈ 5.26 x 10^4 mol/m²
Therefore, at 12 K and a gas pressure of 103 Pa, the surface density of adsorbed molecules is approximately 1.87 x 10^5 mol/m², while at 68 K and the same pressure, the surface density is approximately 5.26 x 10^4 mol/m².