One langmuir corresponds to an exposure of a surface to a...

One langmuir corresponds to an exposure of a surface to a gas at a pressure of $1.00 \times 10^{-6}$ torr for 1 second at $298.15 \mathrm{~K}$. Define one langmuir in units of pascals instead of torr. How many nitrogen molecules will strike a surface of area $1.00 \mathrm{~cm}^{2}$ when exposed to $1.00$ langmuir? (See Problem 29-47.)

Key Concepts

Pressure Conversion

This concept involves converting pressure units from one system to another. In many scientific applications, it is necessary to translate pressures given in torr to pascals (Pa), as the SI unit for pressure is the pascal. The conversion factor—where 1 torr is approximately 133.322 pascals—is used to ensure consistency in calculations, particularly when dealing with physical equations expressed in SI units.

Langmuir Unit

The Langmuir is a specialized unit used in surface science to quantify the exposure of a surface to a gas. It is defined as the product of pressure and time, typically given as exposure to 1.00×10?? torr for 1 second. Changing the units to pascals for pressure involves using conversion factors, but the fundamental concept remains the same—representing a dose of gas molecules contacting a surface.

Kinetic Theory of Gases

This theory provides the framework for understanding the motion of gas molecules and their interactions with surfaces, which is essential when calculating molecular flux. It explains how the average speed of molecules and their number density, which can be derived from the ideal gas law, influence the rate at which molecules collide with a surface.

Molecular Flux Calculation

Molecular flux refers to the number of gas molecules striking a unit area of a surface per unit time. Calculating this flux involves linking the pressure of the gas (adjusted to SI units) to the number density of molecules using the ideal gas law, and then applying principles from kinetic theory. This calculation is crucial for applications in surface reactions, adsorption phenomena, and vacuum technologies.

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