Answer:
Concentration of the resulting solution = 2.04 M
Explanation:
<u>Data:</u>
M1 = 5.10 M
V1 = 200.0 mL
V2 = 500.0 mL
M2 = ?
By modifying the volume of solution, keeping the amount of solute constant, the concentration changes. To perform the calculations, the equation will be:

Where M1 is the initial concentration of the solution, M2 the final concentration and V is the value of the volumes of the initial and final solution.
Clearing the value of M2 from the equation and replacing the values we have:

Answer: 15.0 moles of
are formed from 30.0 mol of 
Explanation:
The balanced chemical reaction is :
According to stoichiometry :
2 moles of
give = 1 mole of 
Thus 30.0 moles of
will give =
of 
Thus 15.0 moles of
are formed from 30.0 mol of 
You will need a periodic table to help you answer this problem. The atomic numbers are arrange from lowest to highest in the periodic table. You can locate element number 55 to be Cesium with an atomic weight of 132.905 amu. So, you start from element 56. The following elements are:
56 Barium 137.328 amu
57 Lanthanium 138.905 amu
58 Cerium 140.116 amu
59 <span>Praseodymium 140.908 amu
60 Neodymium 144.243 amu
Neodymium is already greater than 144 amu. Therefore, these elements only include Barium, Lanthanium, Cerium and Praseodymium.</span>
First, we use avogadro's number to convert atoms into moles. Then, relate the number of moles from elemental to the compound. Lastly, we use conditions at STP to calculate the volume. We do as follows:
<span>9.86 x 10²⁸ O-atoms ( 1 mol / 6.022x10^23 atoms O) ( 1 mol N2O2 / 2 mol O ) ( 22.4 L / 1 mol ) = 1833809.37 L needed</span>