Hi, Jesset!
Great job on problem 1! You correctly identified the formula for diphosphorus pentoxide, and you balanced the equation so there is an equal amount of phosphorus and of oxygen in both in the reactants and products.
Problem 2 needs a second look.
We're starting with 3.25 moles of phosphorus, P4. We'll have to use dimensional analysis to find the number of moles of P2O5 that will generate. Because we're told the O2 is "sufficient...to complete the reaction," it doesn't really play a role in determining how much P2O5 is generated.
To go from moles of one substance to moles of another, we need to use their coefficients from the chemical reaction as a bridge. When you are doing dimensional analysis, you always want the unit you are heading toward in the numerator and the unit you are moving away from in the denominator.
We started with 3.25 moles of P4. We want to move toward moles of P2O5 and away from moles of P4, so we know that moles of P2O5 will be in the numerator of our first comparison and moles of P4 will be in the bottom. The comparison we can make between them is by using the coefficients from the chemical reaction: for every 1 mole of P4 in the reaction, assuming there is enough oxygen, there will be 2 moles of P2O5. So we end up with:
3.25 moles P4 ( 2 moles P2O5 / 1 mole P4)
The math boils down to 3.25 * 2, which is 6.50. Therefore, 6.50 moles of P2O5 will be made from 3.25 moles of P4 and sufficient oxygen.
Good job on problem 3! You nailed that one :)
