1. CH 13 The Chemistry of Gases
Gases are elements (He), elemental substances (O2), or compounds (CO2) in which the particles of the substance are widely separated, moving randomly, and have very little attraction to each other.
Gases
Are fluids
Have low density
Are highly compressible
Fill their container

2. Describing Gases
Aside from the type of gas, there are four physical properties that describe a gas. Each of these properties can have an affect on the others.
They are:
Amount of the gas
Temperature of the gas
Pressure of the gas
Volume of the gas

3. Property 1: Volume
Gases expand to fill the container which contains them.
The volume of a gas is the space it occupies which is typically the space of the container.
Volume is expressed in
Liters, L
Cubic centimeters, cm3
Milliliters, mL
1.0 L = 1000 cm3 = 1000 mL

4. Property 2: Temperature
The temperature of a gas is an indirect measure of the average kinetic energy of the particles.
The higher the temperature, the greater the movement of the gas particles.
Temperature is measure on 3 scales
Fahrenheit, which we will NOT use.
Celsius, which is a relative scale.
Kelvin, which is the absolute temperature scale.
Tk = Tc Tf = [9/5]Tc + 32

5. Property 3: Pressure
The pressure exerted from a gas is a result of the force of the collisions of the gas particles as they strike the sides of the container.
These collisions are elastic (conserve energy).
Pressure is the ratio of force to unit area.

6. Units of Pressure
Atmospheres (atm) defined by the pressure of the atmosphere at sea level which is 1.0 atm.
Pascal (Pa) the metric unit of pressure from the definition of the force of 1.0 N over 1.0 square meters of area.
Pounds per square inch (psi) British unit
1.0 atm = kPa = 14.7 psi

7. The Barometer The barometer measures atmospheric pressure.
The mercury barometer was one of the first apparatus to do this.
The atmosphere can support a column of mercury 760 mm high.
1 atm = 760 mmHg
Also called the Torr after its inventor Torricelli.

8. Aneroid Barometer A more practical barometer is the aneroid barometer.
As pressure changes the vacuumed disc, called the aneroid, expands and contracts.
This indicates relative pressure on a calibrated scale.

9. Property 4: Amount of Gas
The amount of gas present is the actual number of particles in the volume of gas. This is measured in moles (n).
The moles of gas is the mass of the gas divided by the molar mass of the substance.
n = m/M
Particles = n * NA