Lecture08222

Gas State: Basics, Pressure and Its Measurement

Lecture 8

Aristotle’s Elements

Gases

everywhere.

Some important gases

Oxygen O2

Nitrogen N2

Argon Ar

Carbon dioxide CO2

Methane CH4

Ammonia NH3

Chlorine Cl2Ethylene C2H4

Hydrogen H2

Helium

Hydrogen sulfide H2S

Carbon cycle

Gases are important.

All gases

has remarkably similar physical behavior.

The molecules

are much farther apart in the gas

than in either the liquid or the solid.

What distinguishes gases from liquids and solids:

Gas volume changes greatly with pressure.Gas volume changes greatly with temperature.Gases have relatively low viscosity.Most gases have relatively low densities under normal conditions.Gases are miscible.

Pressure (P)

is defined as the force exerted per unit of surface area:

Pressure=Force/Area

Pa=N/m2

Gases exert pressure

on all surfaces with which they make contact.

Evangelista Torricelli (1608-1647), Italian scientist

Torricelli’s experiment

Manometers are devices

used to measure the pressure of a gas in an experiment.

Some widely used manometers

A sample problem

on converting units of pressure.

THE END