Instruction

1

Suppose to you the task: it is necessary to determine

**the mass of**carbon dioxide**gas**occupies at normal pressure and room temperature, the volume of 0.18 m^3. First of all, remember the universal rule that 1 mole of any**gas**at normal conditions occupies a volume equal to 22.4 liters. (More precisely, 22, 414 liters, but to simplify the calculations, this value can be rounded).2

Then move the volume in liters. 0.18 m^3 is 180 liters. Accordingly, it contains 180/22,4 = 8,036 moles of carbon dioxide

**gas**.3

Now remains the last step. Formula of carbonic

**gas**- CO2. Its molar mass: 12 + 16*2 = 44 gram/mol. That is, one mole of carbon dioxide**gas**contains about 44 grams of this substance. How much it 8,036 moles? Perform the multiplication: 44*8,036 = 353, 58 grams or rounded 353,6 grams. The problem is solved.4

If you need to find

**the mass**of the same carbon dioxide**gas**, but under conditions very different from normal? For example, some amount**of gas**placed in a sealed vessel of volume V, is heated to a temperature T, measured his pressure, proved equal to P. Question: what mass of carbon dioxide**gas**contained in the vessel under such conditions?5

And this task is also very simple. To solve it you just have to remember the equation Mendeleev-Clapeyron, named after two outstanding scientists. It was derived by them to describe States of so-called "ideal

**gas**". Its formula is: PV = MRT/m. Or in a slightly modified form: PVm = МRT, where S is the pressure in Pascals, V is the volume in cubic meters, m is the molar mass of**gas**, M is its effective mass, T is the temperature in degrees Kelvin, R is the universal gas constant, approximately equal to 8,31.6

It is easy to see that the actual mass

**of gas**M is calculated by the formula: M = PVm / RT. Substituting in this formula all the known data, and remembering that the molar mass of carbon dioxide**gas**m is equal to 44 grams/mole, you will easily get the answer.7

Of course, neither carbon dioxide nor any other is not an ideal gas. Therefore, the equation Mendeleev-Clapeyron is not quite exactly describes his condition. But if the conditions are not very different from normal, errors of the calculation are small and can be neglected.