Knowing formula gas , its molar mass can be calculated by an elementary calculation.Take carbon dioxide.Its formula - CO2.So its molar mass is as follows: 12 + 32 (molar mass of oxygen based on the index "2») = 44.
Well, if you need to calculate the molar mass an unknown gas , located insome kind of confinement such as a sealed bottle?Here we come to the aid of the universal equation of Clapeyron-Mendeleev, describing the state of the "ideal gas ».Of course, none of the gas does not meet the "ideal", but at a pressure a
nd temperature, slightly different from the normal equation is very convenient for calculations.And the resulting uncertainty in the calculations is very small and it can be safely ignored.
universal equation has the form: PV = MRT / m, where P - pressure gas in Pascals;
V - its volume in cubic meters;
M - actual weight gas ;
m - its molar mass;
R - the universal gas constant;
T - Temperature gas in degrees Kelvin.
You will see that the molar mass is calculated by the formula MRT / PV.For example, it is necessary to find the molar mass gas, if it is known that 3 kilograms of gas are in a sealed container volume of 1.7 cubic meters at a pressure of 100,000 Pa and a temperature of 27 degrees Celsius.
Substitute known values ​​in this formula, of course, do not forget to first convert into a single system of values.Otherwise it will complete nonsense.3.0 * 8.31 * 300/170000 = 0.04399 kg / mol.
Well, since the molar mass of the substance measured in grams per mole, multiply the result by 1000 and get an answer: the molar mass of the gas , located under these conditions is equal to 43.99 grams / mole oras rounded - 44 gram / mole.That is the same carbon dioxide.