Let us take by general case where one molecule of a substance A splits up into n molecule of B on heating i.e.,t = 0 at = teq a x nx Total no. Gas density measurements can be used to determine the degree of dissociation. As the temperature rises, more and more dissociation takes place, and when practically complete dissociation occursthe density reaches its lowest limit.The extent of issociation, ice., the fraction of the total number of molecules which suffers dissociation is called the degree of dissociation. The process is reversible and is called thermal dissociation.Examples :With increase in the number of molecules, the volume increases (pressure remaining constant) and, in consequence, the density decreases. This is due to the splitting of the molecules into simpler ones. The observed densities decrease towards a limit as thetemperature is raised. the measured densities are found to be less than those calculatedfrom their molecular formula. of moles Observed molecular weight or molar mass of the mixtureQ.If the total mass of the mixture in the above case is 300 gm, the moles at C(g) present are.įor certain substances such as ammonium chloride, nitrogen peroxide, phosphorus pentachloride, etc.
Therefore, 756.89 ml of propanol will have the same number of molecules as present in 210 ml of water at 25 degrees Celsius.įor certain substances such as ammonium chloride, nitrogen peroxide, phosphorus pentachloride, etc. Mass of propanol = Number of moles x Molar mass = 11.66 x 60.1 = 700.666 g Number of moles of propanol = Number of molecules/Avogadro's number = 7.022 x 10^24/6.022 x 10^23 = 11.66 moles Molar mass of propanol = 60.1 g/mol (from periodic table) Number of molecules of water = Number of moles x Avogadro's number = 11.67 x 6.022 x 10^23 = 7.022 x 10^24 moleculesĬalculating the volume of propanol with the same number of molecules as water Avogadro's number = 6.022 x 10^23 molecules/mol Number of moles of water = Mass/Molar mass = 210/18 = 11.67 moles Molar mass of water = 18 g/mol (from periodic table) Mass of water = Density x Volume = 1 x 210 = 210 g Calculating the number of molecules in 210 ml of water