Guide
1
Imagine inquisitive king Hiero gave his court mathematician another crown, and ordered: "Here it is precisely because of pure gold.Determine Archimedes, what is the concentration of molecules in it. "Brilliant scientist such a task would put a dead end.Well, you decide it quickly.Suppose the crown would weigh exactly 1.93 kilogram, taking the volume of 100 cm ^ 3.
2
First, find how many moles of gold contained in an amount of substance.With the help of the periodic table, you'll learn yarnuyu molecular weight of gold: 197 amu(atomic mass units).A mass of one mole of any substance (in grams) is numerically equal to its molecular yarnoy weight.Therefore, one mo
le of gold weighs 197 grams.Dividing the actual weight of the crown on the molar mass of gold, you will receive: 1930/197 = 9.79.Or, rounded, 9.8 moles of gold.
3
Multiply the number of moles on the universal Avogadro's number, indicating how many elementary particles contained in a mole of any substance.9.8 * 6.022 * 10 ^ 23 = 5.9 * 10 ^ 24.That's how much molecules about gold contained in the crown.
4
Well, now find concentration molecules simple.100 cubic centimeters - is 0.0001 m ^ 3.Section: 5.9 * 10 ^ 24 / 0.0001 = 5.9 * 10 ^ 28. concentration of molecules of gold is equal to 5.9 x 10 28 / m3.
5
Now suppose that you set such a task: the pressure P, the mean square speed molecules of carbon dioxide to V. required to determine the concentration of molecules his .And there's nothing complicated.There is a so-called fundamental equation of kinetic theory of ideal gas: P = V ^ 2m0C / 3, where C - is the concentration of molecules gas and m0 - mass of one of its molecules s.Therefore, the desired concentration of C is as follows: C = 3P / m0V ^ 2.
6
only unknown quantity - m0.It can be found in the Handbook of Chemistry and Physics.Can also be calculated by the formula: M = m0 / Na, where M - molecular mass of carbon dioxide (44 g / mol) and Na - Avogadro number (6,022h1023).By substituting all the values ​​in the formula, calculate the required concentration S.
7
Modify the condition task.Let you know when the temperature T and the pressure P of carbon dioxide.As these data to find concentration his molecules ?Gas pressure and temperature are related by the formula: P = CkT, where C - concentration gas molecules and K - Boltzmann constant, which is equal to 1.38 x 10 -23.That is, C = P / kT.Substituting in the formula known values, you calculate the concentration S.