Consider the reaction represented by the following equation: C2H4(g) + 302(g) → 2CO2(g) + 2H2O(g)How many…

Analyze the question: We are given a balanced combustion equation and asked how many moles of ethene (C₂H₄) must burn to give 0.1 mole of water.

Concept: The coefficients in a balanced equation give the mole ratio of reactants and products.

C₂H₄(g) + 3O₂(g) → 2CO₂(g) + 2H₂O(g)

(The "302" in the question is just a typing error for 3O₂.)

Solution:

From the equation:

• 1 mole of C₂H₄ produces 2 moles of H₂O

So the mole ratio is C₂H₄ : H₂O = 1 : 2.

Moles of C₂H₄ = (1/2) × moles of H₂O = (1/2) × 0.1 = 0.05 mole

Check: If 0.05 mole of ethene burns, then 2 × 0.05 = 0.10 mole of water forms. ✔

Tip: In stoichiometry questions, first make sure the equation is balanced, then write the ratio of the two substances in the question (here 1 : 2). Multiply or divide by that ratio. Since water has the larger coefficient, you need fewer moles of ethene than the moles of water, so the answer must be smaller than 0.1. That alone rules out B, C, and D.