Problem 36 - Chemistry: An Atoms-Focused Approach

Question

Why does atmospheric pressure decrease with increasing elevation?

Step-by-Step Solution

Answer

Answer: Atmospheric pressure decreases with increasing elevation due to the reduced weight of the overlying air and the decreasing molecular density of the air. As elevation increases, there is less air above a given point, leading to a decrease in atmospheric pressure. Additionally, the air becomes less dense at higher elevations, further reducing atmospheric pressure by having fewer air molecules exerting force on the same point.

Step 1: Define Atmospheric Pressure

Atmospheric pressure is the force exerted by the weight of the air above a given point on the Earth's surface. It is measured in units of pressure, such as Pascals (Pa), which represent the force exerted per unit area.

Step 2: Introduce the Weight of the Air and Molecular Density

The weight of the air above a specific point on the Earth's surface is determined by the mass of the air and the gravitational force acting on it. Molecular density refers to the number of air molecules in a given volume (per unit volume) and can be affected by factors such as temperature, pressure, and elevation.

Step 3: Discuss the Effect of Elevation on Molecular Density

As elevation increases, the distance from the Earth's surface also increases, which means there is less air above a given point. As a result, the weight of the overlying air decreases, and this causes a decrease in atmospheric pressure. Additionally, as elevation increases, the air becomes less dense due to lower pressure and lower temperatures. This causes the number of air molecules per unit volume to decrease, further reducing the weight of the overlying air and leading to a lower atmospheric pressure.

Step 4: Explain the Relationship Between Atmospheric Pressure and Elevation

Atmospheric pressure decreases with increasing elevation due to two primary factors: the decreasing weight of the overlying air and the decreasing molecular density of the air. As elevation increases, there is less air above a given point, leading to a decrease in atmospheric pressure because lesser mass of air is exerting force on a given point. Additionally, the air becomes less dense, further reducing atmospheric pressure by having fewer air molecules exerting force on the same point. Together, these factors cause a decrease in atmospheric pressure with increasing elevation.

Step 5: Summarize the Explanation

In summary, atmospheric pressure decreases with increasing elevation because there is less air above a given point, resulting in a decrease in the weight of the overlying air, as well as decreasing molecular density caused by lower temperature and pressure. Both of these factors cause a decrease in atmospheric pressure as elevation increases.