WEBVTT

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Here is the problem: Balance the chemical equation C3H8 plus O2 → CO2 plus H2O.

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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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So the answer is C3H8 plus 5O2 → 3CO2 plus 4H2O.

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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: 3 equals 3, H: 8 equals 8, O: 10 equals 10, which checks out.