The Langmuir adsorption isotherm equation can be used to determine the fraction of the surface covered by the gas molecules at a certain pressure P. The equation is: = K * P / 1 + K * P where is the fraction of the surface covered by the gas molecules, K is the Langmuir constant, and P is the pressure.To find the fraction of the surface covered by the gas molecules at the given pressure P, simply plug in the values of K and P into the equation: = K * P / 1 + K * P This will give you the fraction of the surface covered by the gas molecules at that specific pressure.