Reviewed CSCA Chemistry question · Easy

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

CuS(s) + O2(g) → CuO(s) + SO2(g)
2CuS(s) + 3O2(g) → 2CuO(s) + 2SO2(g)
CuS(s) + 2O2(g) → CuO(s) + SO2(g)
2CuS(s) + O2(g) → 2CuO(s) + SO2(g)

Show the answer and explanation

Correct answer

B. 2CuS(s) + 3O2(g) → 2CuO(s) + 2SO2(g)

Principle or equation

A balanced chemical equation must have the same number of each type of atom on both sides. Coefficients are adjusted to achieve this.

Why this answer is correct

Start with CuS + O2 → CuO + SO2. Balance Cu and S: already one each. Balance O: left has 2 O atoms, right has 3 (1 in CuO + 2 in SO2). Multiply all by 2: 2CuS + 3O2 → 2CuO + 2SO2. Now left has 2 Cu, 2 S, 6 O; right has 2 Cu, 2 S, 6 O. Balanced.

Example

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

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