Ace Your Dual Enrollment Physical Science Midterm 2026 – Ignite Your Inner Scientist!

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In the reaction 2 H2 + O2 -> 2 H2O, given 4.0 g H2 and 32.0 g O2, which reactant is limiting and how many grams of H2O can be produced?

H2 is limiting; about 35.7 g of H2O can be produced

The amount of product is limited by the reactant that runs out first, which you find by comparing the amounts available to what the reaction needs in moles. The equation shows a 2:1 ratio of hydrogen to oxygen, and a 2:2 (1:1) relationship between hydrogen and water.

Convert masses to moles: hydrogen is 4.0 g ÷ 2.016 g/mol ≈ 1.984 mol. oxygen is 32.0 g ÷ 32.00 g/mol = 1.00 mol. For 1.00 mol of O2, you’d need 2.00 mol of H2, but you only have about 1.984 mol H2, so hydrogen runs out first. That makes hydrogen the limiting reactant.

With hydrogen limiting, the amount of water produced equals the amount of hydrogen consumed, in a 1:1 mole ratio. So moles of water formed ≈ 1.984 mol, which is 1.984 mol × 18.015 g/mol ≈ 35.7 g of H2O.

O2 is limiting; about 35.7 g of H2O can be produced

H2 is limiting; about 44.8 g of H2O can be produced

O2 is limiting; about 63.0 g of H2O can be produced

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Ace Your Dual Enrollment Physical Science Midterm 2026 – Ignite Your Inner Scientist!

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