Dalton's Law of Partial Pressure

Pressure is the force applied by the particles of a gas colliding with a surface such as the walls of a container.  If there is a mixture of gases, each individual type of gas particle will exert a pressure.  This is partial pressure, or the pressure exerted by a specific component of a gas mixture.

Dalton's Law of Partial Pressure states that the total pressure exerted by a mixture of gases will be the sum of the individual pressures of each of its components.

This concept can be combined with the ideal gas law to solve for the total pressure in a gas mixture.

Molar Volume and Avogadro's Principle

Avogadro's Principle states that equal volumes of gases at equal temperature and pressure, will contain the same number of particles.  Therefore now we can have a molar volume, just as we have a molar mass.

The molar volume of any gas at STP is 22.4 L.  This can be determined by using the ideal gas law.
REMEMBER! This only applies to a GAS at STP.

We can now apply this concept to chemical reactions.  If a reaction takes place at constant temperature and pressure, the ratio of all the gases (reactants and products) will be the same as the mole ratio.

Molar Volume and Avogadro's Principle

Avogadro's Principle states that equal volumes of gases at equal temperature and pressure, will contain the same number of particles.  Therefore now we can have a molar volume, just as we have a molar mass.

The molar volume of any gas at STP is 22.4 L.  This can be determined by using the ideal gas law.
REMEMBER! This only applies to a GAS at STP.

We can now apply this concept to chemical reactions.  If a reaction takes place at constant temperature and pressure, the ratio of all the gases (reactants and products) will be the same as the mole ratio.

Ideal Gas Law

In Ideal Gas Law calculations there is only one set of conditions (P,V,T), but we've added the idea of mass.

Combined Gas Laws

If the number of gas particles does not change, the pressure, volume and temperature will always combine to form a constant.  Because of this, the pressure times the volume and divided by the Kelvin temperature always be equal.  1 represents the initial conditions and 2 is the final conditions.

This is called the Combined Gas Law

By holding one of the three conditions constant, we can look at the relationship between any 2 of the variables.

Boyle's Law stated that if temperature is held constant, the pressure and volume for a sample of gas will be inversely proportional.  In other words, if the kinetic energy of a system is held constant, the force applied by its particles will be inversely proportional to the size of the container.  If the particles are moving at the same speed and the volume is decreased, the particles will hit the walls more often and apply more force.  If the volume is increased, the pressure will decrease.

Charles' Law states that if pressure is held constant, the volume and temperature will be directly proportional.  In other words, if the force applied by the particles on the walls of their container is constant, changes in the space occupied by the gas and their average kinetic energy must be directly proportional.  If you increase the temperature of a sample of gas, the particles will move faster.  To maintain a constant pressure (force on the walls), the container must get bigger.

Gay-Lussac's Law states that if the volume is held constant, the pressure and temperature must be directly proportional.  In other words, if the amount of space is constant (the container can't get bigger or smaller), if the particles move faster (temperature increases) they will have to collide with the walls of their container more, therefore more force.

Calculations:

1. Label all given information. (P, T or V and 1 or 2)
   Remember it really doesn't matter what you label 1 or 2, but it IS IMPORTANT that you keep the SET of conditions together.
2. Choose the correct formula and solve for the unknown algebraically.
3. Substitute in the given information using both the value and UNIT.  Be careful to substitute the correct values 1 and 2 and to cancel the units.  You may need to use a conversion to make the units cancel.
4. Don't forget that STP means Standard Temperature and Pressure.  These are a set of conditions!
5. Don't forget that temperature must ALWAYS be in Kelvin.
   To convert Celsius to Kelvin, add 273.  To return to Celsius from Kelvin, subtract 273.

Standard Conditions: Pressure

For gas laws, standard pressure is considered the average pressure at sea level or 1 atmosphere (atm).

There are several other units used for pressure.

Using a barometer with mercury, standard atmospheric pressure will support a column of mercury 760 mm high.  This became a unit, or  mmHg.  Another name for mmHg is torr.

1 atm = 760 mmHg = 760 torrs

The SI unit is the pascal (Pa) which is equal to 1 Newton/meter² . 

1 atm = 101.325 kiloPascals (kPa)

Standard Conditions: Temperature

For gases, standard temperature is considered the freezing point of water, 0˚C.  This causes a problem with mathematical calculations.  Temperature can be positive, negative or 0.  A positive ratio can't equal a negative number, and multiplying or dividing by 0 is 0 or undefined respectively.  To avoid this mathematical problem, the Celsius scale was shifted down to absolute zero. By using linear regression and Charles' Law, it is possible to determine the coldest possible temperature, or  -273.15˚C.

This new scale was called the Kelvin scale in honor of Lord Kelvin.  The gradations of the Kelvin scale are exactly the same as on the Celsius scale, the only difference is that 0 has been shifted to -273.  Therefore there are no negative values on the Kelvin scale.

Temperature is a measurement of the average kinetic energy of the particles of a substance.  If the lowest possible temperature is -273.15˚C, that means that the average kinetic energy must be 0, or that all molecular motion stops.

ALL CALCULATIONS IN GAS LAWS MUST ALWAYS BE CONVERTED TO KELVIN. To convert a Celsius temperature into Kelvin, just add 273.  To convert back from Kelvin to Celsius, just subtract 273.  *Note- by convention the degree symbol is not used for Kelvin.