14.1. Gas Properties http://www.ck12.org
14.1 Gas Properties
Lesson Objectives
- List some substances that are gases at 25°C and some characteristics that they have in common.
- Define and give examples of diatomic gases.
- Describe how pressure is measured, and be able to carry out conversions between different units of pressure.
Lesson Vocabulary
- diatomic gas: Any two-atom molecules that exist in the gas phase around room temperature.
- pressure: A measure of the total amount of force divided by the surface area over which it is exerted.
- barometer: An instrument used to measure pressure.
- atmospheric pressure: The pressure exerted by the weight of the atmosphere at a given altitude.
- millimeters of mercury (mm Hg): A common unit of pressure originating from the mercury barometer.
- torr: A unit of pressure equal to mm Hg named after Italian physicist Evangelista Torricelli.
Check Your Understanding
- What evidence might there be to demonstrate the presence of gases in our atmosphere?
- Can you think of examples from your life suggesting that there are gases we depend on for survival?
Introduction
Figure14.1 shows a nitrogen gas discharge lamp, where nitrogen gas is energized to produce light that appears
lavender in color. Nitrogen gas is the most abundant gas on Earth. However, despite the fact that approximately
78% of the air we breathe is nitrogen, we may hardly notice it as we navigate our daily lives. Although nitrogen-
containing compounds have been known since ancient times, pure elemental nitrogen in its gaseous form was not
discovered until 1772, by Daniel Rutherford. This discovery, along with Joseph Priestley’s discovery of oxygen in
1774, greatly influenced our modern understanding of gases and matter in general.
Nitrogen has a melting point of -210°C and a boiling point of -196°C. It is colorless, odorless, tasteless, and fairly
unreactive at normal temperatures and pressures. It exists as N 2 molecules, in which two nitrogen atoms are held
together by a strong triple covalent bond. Its lack of reactivity is derived from the large amount of energy that would
be required to break this bond. Nitrogen is an example of adiatomic gas, which refers to any two-atom molecules
that exist in the gas phase around room temperature.
In this lesson, we are going to study some properties exhibited by gases, with a special focus on the pressure they
exert and how pressure is measured.