Gas Laws
In gases there are three different variables, which are pressure, temperature and volume, and all of these components are dependent on each other.
If one of these components is fixed and any of the other two are changed, the last component would also change with respect to the variable component. This can be seen in the following three relationships:
If the temperature is kept constant the relationship between Volume and Pressure would be an inversely proportional relationship, showing that when one component is increased, the other one would decrease. This can be seen in the following relationship:
which can be depicted as a graph as:
The equation can also be rearranged to give:
If the volume is kept constant the relationship between Pressure and temperature would be a directly proportional relationship, indicating that one component increases, the other would decrease. This can be seen in the following relationship:
Which can also be written as:
If the pressure is kept constant the relationship between volume and temperature would be a directly proportional relationship, indicating that one component increases, the other would decrease. This can be seen in the following relationship:
Which can also be written as:
On combining these three equations two very important equations can be derived:
and
Where R 8.314kJ mol-1 is the gas constant and n is the number of moles.
The units for each of Pressure, Volume and Temperature are Pa, m3 and K respectively.
Now if this equation is analysed one can state that n is the number of moles, and therefore this can be said to be m/M (mass/Molecular mass) and thus the molecular mass can be found with the following equation:
It must be noted that this equation cannot be used for solids but it can be only used for volatile liquids and gases. For volatile liquids, the temperature would have to be increased so that the volatile liquid would turn into a gas. All volume measurements should be collected in a gas syringe.
Gay Lussac’s Law
Another important concept is the Gay Lussac’s Law of combining of volumes which states that when two different volumes are mixed the ratio of these two volumes would be proportional to the original ratio under the same pressure and temperature. If these two gases react the volume ratio between the original reactants and the final products would then depend on the stoichiometry of the reaction.