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Here is the problem: In the reaction C6H12O6 plus O2 → CO2 plus H2O, how many grams of H2O form from 90 g of C6H12O6?

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Balance atoms of every element, then use the coefficients as mole ratios.

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Write an atom balance for each element. Give each species an unknown coefficient; atoms of every element must be equal on both sides.

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Solve the linear system with the smallest whole numbers. Exact elimination leaves one free coefficient; scaling by the least common denominator gives integers.

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Balanced equation.

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Moles of C6H12O6.

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H2O via the mole ratio 6: 1.

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So the answer is C6H12O6 plus 6O2 → 6CO2 plus 6H2O; 90 g C6H12O6 → H2O: 53.9982 g (2.9974 mol).

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Coefficients in a balanced equation count particles (moles), not grams. Convert grams to moles, apply the mole ratio, then convert back to grams with the other species prime molar mass. Assumes the reaction goes to completion with the known species fully consumed (or formed).

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C: 6 equals 6, H: 12 equals 12, O: 18 equals 18, which checks out.

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H2O is produced in a 6: 1 mole ratio to C6H12O6.