Chapter 9 Gases

.

Figure 9.1  A visualization of the carbon dioxide and methane added to the atmosphere on a global scale over 2021. (credit: NASA Scientific Visualization Studio, https://svs.gsfc.nasa.gov/5116)

We are surrounded by an ocean of gas—the atmosphere—made up of nitrogen (N₂, 78.1%), oxygen (O₂, 21.0%), and argon (Ar, 0.9%). However, the gases that play essential roles in our planet’s health and well-being exist at only trace levels. For example, carbon dioxide (CO₂, 0.0429%) and methane (CH₄, 0.0001%) (Figure 9.1) participate in the greenhouse effect (see section 9.5 for more information) that has kept Earth at a habitable temperature for millions of years. Now these concentrations are accelerating due to human activity. Ozone (O₃, 0.000001 – 0.0001%) can protect us from harmful ultraviolet (UV) radition when it is in the stratosphere or contribute to asthma and decrease crop yields when it is near Earth’s surface in the troposphere.

Many of the properties of gases are familiar to us from our daily activities. Heated air rises – like to the ceiling of a room – because the warm gas has more kinetic energy and expands thus lowering its density compared to the surrounding air. This lower denisty creates the buoyancy that makes the air rise. The rising of warm air in the atmosphere is what drives convection and weather events on our planet.

In this chapter, we will examine the relationships between gas temperature, pressure, amount, and volume. We will study a simple theoretical model and use it to analyze the experimental behavior of gases. The results of these analyses will show us the limitations of the theory and how to improve on it.