Gases and Atmospheric Chemistry

Gas Pressure
Gas Pressure is defined as a force per unit area.

SI Units (System International) are in Kilopascals (kPa).

List of Pressure and their Corresponding Units
1 atmosphere (atm) is equal to: All of the previous units are of standard pressure.
 * 101.3 kPa
 * 760 millmeters (mm)
 * 29.9 inches of mercury
 * 14.7 pounds per square inch (psi)

Temperature
Standard temperature = 0ºC or 273 Kelvin

Kelvin-Celsius conversion: 0ºC + 273 = Kelvin

Standard Temperature and Pressure is abbreviated to STP

Molar Volume
Fixed amounts of gases occupy the same volume as long as the temperature and pressure are the same. Thus we can say that 1 mole is equal to the molar mass that contains 6.02 × 1023, which occupies 22.4 L.
 * The volume occupied by 1 mole of oxygen gas at STP is found to be 22.4 Liters.

Boyle's Law:
The Volume of a fixed mass of gas is inversely proportional to its pressure provided the temperature remains constant.

Mathematically:
 * $$PV=constant\,$$

or written as:
 * $$P_1V_1=P_2V_2\,$$

Charles' Law
The volume of a fixed mass of gas is directly proportional to its temperature (in Kelvin), provided the pressure remain constant.

Mathematically:
 * $$ \qquad \frac {V}{T} = constant $$

or written as:
 * $$ \qquad \frac {V_1}{T_1} = \frac {V_2}{T_2} $$

Gay-Lussar's Law
The pressure of a fixed mass of gas is directly proportional to the Kelvin temperature, provided the volume remains constant

Mathematically:
 * $$ \qquad \frac {P}{T} = constant $$

or written as:
 * $$ \qquad \frac {P_1}{T_1} = \frac {P_2}{T_2} $$

Combined Gas Law

 * $$ \qquad \frac {p_1V_1}{T_1}= \frac {p_2V_2}{T_2} $$

e.g A gas has volume of 115mL at STP. Find the volume at 75.2 kPa.


 * $$ V_1 = 115mL$$
 * $$ T_1 = 0º C = 273K$$
 * $$ P_1 = 101.3kPa$$
 * $$ V_2 = ?$$
 * $$ T_2 = 50º C = 323K$$
 * $$ P_2 = 75.2kPa$$


 * $$ V_2 = \frac {p_1V_1}{T_1P2}= \frac {(101.3kPa)(115mL)(328K)}{(273K)(75.2kPa)} = 183.3mL$$

Ideal Gas Law
The ideal gas is a hypothetical gas composed of particles that have zero size, travel in straight lines, and have no attraction to each otehr (zero intermolecular force).

Ideal Gas Equation
The equation is:
 * $$PV=nRT\,$$

P = Pressure

V = Volume (liters)

n = moles

T = Temperature (Kelvin)

R = Ideal gas constant

Ideal Gas Constant
e.g How many moles of O2 are present if the volume of the gas is 274mL at a pressure of 120 kPa and a temperature of 75ºC?
 * $$ V = 274mL$$
 * $$ P = 120kPa$$
 * $$ T = 75ºC + 273 = 348K$$
 * $$ n = ?$$
 * $$ R = 8.32 L * kPa / mol * k$$


 * $$PV=nRT\,$$


 * $$ n = \frac {(120kPa)(0.274K)}{(8.32 \frac {k · kPa}{mol · k})(344k)}$$


 * $$ n = 0.0114 mol\,$$