The reaction is
2Cu + S → Cu2S
So as per balanced given reaction we need one mole of sulphur over two moles of copper
Or
To react with one mole of sulphur we need two moles of copper
Thus we can say that the mole ration required for complete reaction will be
Cu : S = 2 : 1
As per the given problem the moles of each Cu and S are 3 moles
Thus for each three moles of given sulphur we need six moles of Cu to give three moles of Cu2S
However we have only three moles of copper available
So the limiting reagent is copper
It is going to decide the actual yield of reaction
The three moles of Copper will get completely utilized and only 1.5 moles of S will be used in the reaction making S an excess reagent
The moles of S left will be = 1.5 moles
moles of Cu2S formed = 1.5 moles
