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Reviewed CSCA Chemistry question · Standard

Which of the following equations is correctly balanced for the reaction between solid zinc sulfide and oxygen gas to produce solid zinc oxide and sulfur dioxide gas?

  1. ZnS + O2 -> ZnO + SO2
  2. 2ZnS + 3O2 -> 2ZnO + 2SO2
  3. 2ZnS + 2O2 -> 2ZnO + SO2
  4. ZnS + 2O2 -> ZnO + SO2
Show the answer and explanation

Correct answer

B. 2ZnS + 3O2 -> 2ZnO + 2SO2

Principle or equation

Balancing chemical equations requires equal numbers of each atom on both sides.

Why this answer is correct

Start with ZnS + O2 -> ZnO + SO2. Balance Zn: already 1 each. Balance S: 1 each. Balance O: left has 2, right has 3 (1 in ZnO + 2 in SO2). Multiply O2 by 3/2 to get 3 O on left, then multiply all coefficients by 2 to get whole numbers: 2ZnS + 3O2 -> 2ZnO + 2SO2. Check: Zn 2=2, S 2=2, O 6=6.

Example

For combustion of methane: CH4 + 2O2 -> CO2 + 2H2O.

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