Concentration of particles is the size showing how many particles of substance are in any volume. It is calculated on a formula: c = N/V, its dimension 1/м^3. Often there is a need to define concentration of molecules, and the studied substance can be in any aggregate state: firm, liquid or gaseous.
Instruction
1. Present that the inquisitive tsar Giyeron gave to the court mathematician one more crown, having ordered: "Here it precisely from pure gold. Define, Archimedes what concentration of molecules in it". The ingenious scientist such task would nonplus. Well, and you solve it very quickly. Let's assume, the crown would weigh exactly 1.93 kilograms, occupying at the same time volume in 100 см^3.
2. First of all find how many moths of gold contain in such amount of substance. By means of Mendeleyev's table you learn the molecular mass of gold: 197 and. e. m (atomic units of mass). And the mass of one of any substance (in grams) it is in number equal to its molecular weight. Therefore, one mol of gold weighs 197 grams. Having divided the actual mass of a crown into the molar mass of gold, you receive: 1930/197 = 9.79. Or, in round figures, 9.8 moths of gold.
3. Increase number of moles by the universal number of Avogadro showing how many elementary particles contain in a pier of any substance. 9.8*6.022*10^23 = 5.9*10^24. Here how many molecules of gold approximately contain in a crown.
4. Well, and now to find concentration of molecules as easy as shelling pears. 100 cubic centimeters are 0.0001 м^3. Let's divide: 5.9*10^24/0.0001 = 5.9*10^28. Concentration of molecules of gold is equal 5.9*10^28/м3.
5. Now we will assume that to you such task is set: with a pressure of P, the average square velocity of the molecules of carbon dioxide is equal to V. It is required to define concentration of its molecules. And there is nothing difficult. There is a so-called main equation of the kinetic theory of ideal gas: Р = V^2m0C/3, where C – concentration of molecules of gas, and m0 – the mass of one its molecule. Therefore, required concentration With is so: With = 3P/m0V^2.
6. The only unknown size – m0. She can be recognized in the reference book on chemistry or physics. It is also possible to calculate on a formula: m0 = M/Na, where M – the molar mass of carbon dioxide (44 grams/mol), and Na – Avogadro's number (6.022х1023). Having substituted all sizes in a formula, calculate required concentration of Page.
7. Alter a statement of the problem. Let's assume, only temperature of T and pressure P carbon dioxide are known to you. How according to these data to find concentration of its molecules? Pressure and temperature of gas are connected by a formula: P = CkT, where With – concentration of molecules of gas, and To – Boltzmann's constant equal 1.38*10^-23. That is With = P/kT. Having substituted the known sizes in a formula, you calculate concentration of Page.