Page 53 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

Chapter 2
Basic Properties of Gases

The purpose of this chapter is to describe some basic properties of gases, which are
applicable to not only air but also gaseous air emissions.
The terms gas and vapor are both used to describe the gaseous state of a substance.
However, gas is primarily for a pure substance or mixture that exists in gaseous state
under normal conditions. Vapor is used to describe a substance that is in gaseous state,
which exists in liquid or solid state under normal conditions. A gas can be compressed
above the atmospheric pressure and even nontoxic gases can be lethal when their
concentrations are high enough to displace too much oxygen in the air. While too
much vapor will result in the phase change from gas to liquid by condensation.
Gaseous air emissions can be divided into organic and inorganic types. Organic
compound includes most chemicals based on a structure of carbon atoms. Organic air
emissions include such gases as methane, but the majorities are vapors under normal
conditions. Inorganic gaseous air emissions are primarily gases, except for mercury.
Despite the differences in gas and vapor, they also share some common prop-
erties. Therefore, within this text, gas is used to include vapor unless otherwise
stated.

2.1 Gas Kinetics

Kinetic theory is also known as kinetic molecular theory or collision theory. Kinetic
theory of gases attempts to explain macroscopic properties of gases, such as
pressure, temperature, or volume, by considering their microscopic compositions
and motion. In the kinetic theory of gases, the following assumptions are made
• Gas molecules are considered uniform spherical particles, each of which has a
mass but negligible volume compared to the gas container.
• The number of molecules is large and thus their behaviors can be analyzed
statistically.
• Gas molecules move rapidly, constantly, and randomly. The collision between
the molecules and the wall is considered perfectly elastic and instantaneous.
• The average distance between the gas molecules is large compared to their size.
© Springer Science+Business Media Singapore 2014 27
Z. Tan, Air Pollution and Greenhouse Gases, Green Energy and Technology,
DOI 10.1007/978-981-287-212-8_2