what amounts of each species is expected to be present?

Question

 2.5 g of solid aluminum and 2.5 g of gaseous oxygen react in a combination reaction to produce aluminum oxide. At the end of the experiment, what amounts of each species is expected to be present?

Answer 1

Write a correctly balanced equation for the reaction taking place:

4Al(s) + 3O₂(g) ==> 2Al₂O₃(s) ... balanced equation

Find limiting reactant:

2.5 g Al x 1 mol Al/26.98 g = 0.0927 moles Al

2.5 g O₂ x 1 mol O₂/32 g = 0.0781 moles O₂

If you divide the moles of each reactant by their respective coefficient in the balanced equation, you can find the limiting reactant.

For Al we have 0.0927/4 = 0.0231

For O2 we have 0.0781/3 = 0.0260

So, Al is the limiting reactant

Theoretical yield of Al₂O₃ = 0.0927 mol Al x 2 mol Al₂O₃/4 mol Al x 102 g Al₂O₃/mol = 4.73 g Al₂O₃

O₂ used up during the reaction = 0.0927 mol Al x 3 mol O₂/4 mol Al = 0.0695 mol O₂ used up

O₂ remaining = 0.0781 mol - 0.0695 mol = 0.0086 moles O₂ left over

mass O₂ remaining = 0.0086 mol O₂ x 32 g/mol = 0.275 g O₂

SUMMARY OF AMOUNTS OF EACH SPECIES PRESENT:

4.73 g of Al₂O₃

0.275 g of O₂

0 g of Al