Chemistry Questions?

Question

6Mg + P4 ---> 2Mg3P2

I have 2.5 moles of Mg. How many moles of P4 do I need in this reaction to completely use up all of this Mg?




4Cu(s) + O2(g) ---> 2Cu2O(s)

How many grams of Cu2O will be produced if I react 4.8 grams of copper metal with excess oxygen gas?

Answer 1

Q1] The reaction is already balanced so you just need to know that the reactants are used in the same ratios as in the balanced equation (that is why we balance the equations; to be able to calculate quantities of reactants needed or products created).

You can easily see we need 6 x as much Mg as P4 so just set up the equation:

2.5mole x (1/6) = 0.417moles P4

Note that a mole of P4 contains 4 moles of P

Q2] The equation is already balanced; and since you are told oxygen is in excess, we know copper is the limiting reagent. You need: moles of copper x the ratio of Cu2O/Cu in balanced equation x molecular weight of Cu2O.

(4.8g/63.55g/mol) x 2/4 [2 x 63.55 + 16.0]g/mol = 5.40g