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When zinc sulfide is heated in the presence of oxygen the following reaction occurs: ...

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tdj4325 | (Level 1) Salutatorian

Posted June 20, 2012 at 7:50 PM via web

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When zinc sulfide is heated in the presence of oxygen the following reaction occurs:  ZnS + O2 → ZnO + SO2. If 1.72 mol of ZnS is heated in the presence of 3.04 mol of O2, which reactant will be the limiting reactant?

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chaobas | College Teacher | (Level 1) Valedictorian

Posted June 20, 2012 at 10:01 PM (Answer #1)

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limiting reactant are the one which is completely utilised in the reaction.


ZnS + O2 → ZnO + SO2


The molar ratio is 1 ZnS: 1 O2. That is 1 mole of ZnS combines with 1 mole of O2.

So 1.72 mol ZnS will combine with 1.72 mole of O2.

But there 3.04 mol O2 are present in the mixture. So ZnS is the limiting reagent

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted June 21, 2012 at 1:13 PM (Answer #2)

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The limiting reactant in a chemical equation is the reactant that is completely consumed when the chemical reaction takes place. As a result the reactant determines for how long the reaction takes place.

The reaction between zinc sulphide and oxygen gives zinc oxide and sulfur dioxide.

The chemical equation of the reaction is:

2ZnS + 3O2 → 2ZnO + 2SO2

2 moles of ZnS react with 3 moles of O2 to form 2 moles of ZnO and 2 moles of SO2.

For both the reactants to be totally consumed the ratio of the number of moles of ZnS available to the number of moles of O2 available should be 2/3 = 0.66. The ratio of the moles of the reactants available is 1.72/3.04 = 0.56. This is less than 0.66 showing that there is a lesser amount of ZnS available than required. As a result the limiting reactant is ZnS.


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