Chapter 19, Problem 19.58E

Knudsen effusion cells are used to determine vapor pressures of high-temperature materials. For example, a Knudsen cell is filled with tungsten and heated to $4500\text{K}$ in a vacuum. Measurements show that the cell loses mass $-$ assumed to be $\text{W}$ vapor $-$ at the rate of $\text{2}\text{.113}\text{grams}\text{per}\text{hour}$ out of a hole that is $1.00{\text{mm}}^2$ in area. Calculate the vapor pressure of $\text{W}$ at $4500\text{K}$.