Hi, I'd love some help with this question:
Calculate the number of nitrogen molecules needed to react with oxygen to produce 3.5x10^21 molecules of N2O5
Thanks so much in advance 
Begin by writing a balanced equation for this reaction. This would be 2N
2 + 5O
2 ---> 2N
2O
5Then since you're given the number of molecules of 2N
2O
5 you can find out the number of moles of 2N
2O
5 present using the relation N(number of particles) = n(number of moles) * Na(avogadro's number)
Using this n(number of moles) = 3.5*10^21 / 6.02* 10^23
= 5.81 * 10^-3 moles of 2N
2O
5Now that you have the number of moles, use mole to mole ratios to calculate the number of mole of nitrogen molecules. Therefore the number of moles of nitrogen molecules is = 5.81 * 10^-3 (since there are two moles of 2N
2O
5 produced for every 2 moles of nitrogen molecules)
Now that you have the number of moles of nitrogen molecules, Use N = n * Na to find the number of nitrogen molecules. N = 5.81 * 10^-3 * 6.02 * 10^23 this is = to 3.5* 10^21. So it's the same amount of nitrogen molecules required to produce 2N
2O
5