Zinc sulfide reacts with oxygen according to the reaction: 2ZnS(s) 3O2(g)→2ZnO(s) 2SO2(g) A reaction mixture initially contains 3.0 mol ZnS and 5.2 mol O2. Part A Once the reaction has occurred as completely as possible, what amount (in moles) of the excess reactant is left

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Answer:

There will remain 0.7 moles of O2 in excess

Explanation:

Step 1: The balanced equation

2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g)

Step 2: Given data

Number of moles of ZnS = 3.0 mol

Number of moles of O2 = 5.2 mol

Molar mass ZnS = 97.47 g/mol

Molar mass of O2 =32 g/mol

Step 3: Calculate limiting reactant

For 2 moles of ZnS consumed, we need 3 moles of O2 to produce 2 moles of ZnO and 2 moles of SO2

ZnS is the limiting reactant. It will completely be consumed. ( 3.0 moles). O2 is the reactant in excess. There will be consumed 3.0 mol * 3/2 = 4.5 mol

There will remain 5.2 - 4.5 = 0.7 moles of O2

There will be produced 3 moles of ZnO and 3 moles of SO2

The amount (in moles) of the excess reactant remaining from the reaction is 0.7 mole

Balanced equation

2ZnS + 3O₂ → 2ZnO + 2SO₂

From the balanced equation above,

2 moles of ZnS reacted with 3 moles of O₂

How to determine the excess reactant

From the balanced equation above,

2 moles of ZnS reacted with 3 moles of O₂

Therefore,

3 moles of ZnS will react with = (3 × 3) / 2 = 4.5 moles of O₂

Thus, only 4.5 moles out of 5.2 moles of O₂ is needed to reacted completely with 3 moles of ZnS.

Therefore, ZnS is the limiting reactant and O₂ is the excess reactant.

How to determine the amount remaining

  • Mole of O₂ given = 5.2 moles
  • Mole of O₂ that reacted = 4.5 moles
  • Amount of O₂ remaining =?

Amount of O₂ remaining = 5.2 – 4.5

Amount of O₂ remaining = 0.7 mole

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