[johnnyjohn993]

Bornite ( 2Cu₃FeS₃ )

2Cu₃FeS₃ + 7O₂  6Cu +2FeO + 6SO₂

If 2.50 metric tons of bornite is reacted with excess O₂ and the process has an 86.3% yield of copper , what mass of copper is produced? 

MY SOLUTION:

I got 0.871 tons of O₂ using the stoichiometric relation of bornite and Oxygen.
Then I used the amount of Oxygen (i.e 0.817 tons O₂) to evaluate the the mass of Cu... (by means of stoichiometric relation again) and I got 1.39 tons of Cu.

Question : HOw do I use the 86.3 % yield of copper in getting the right answer.

[Borek]

If there is an excess of oxygen it means all bornite reacted - and you don't have to calculate amount of oxygen. Also, you can calculate theoretical yield of copper directly from the given amount of bornite, not through the oxygen - while the final results are equivalent and shoudl be identical, you just did two times more work than necessary.

1.39 tons is a theoretical yield. Real yield is 86.3% of that. Just multiply.

[Dan]

See also: http://en.wikipedia.org/wiki/Yield_(chemistry)