Stoichiometry Fundamentals

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Stoichiometry Noun

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[stoy-kee-om-i-tree]

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Stoichiometry

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The calculation of quantities, such as mass or moles, of reactants and products involved in a chemical reaction.

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Example: This image shows a chemical reaction where atoms in the reactants (left) rearrange to form the products (right), demonstrating that atoms are conserved.

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Reactant Noun

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[ree-ak-tuhnt]

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Reactant

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A substance that takes part in and undergoes change during a chemical reaction, found on the left side of an equation.

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Example: This diagram shows that reactants, like methane and oxygen, are the starting substances on the left side of a chemical reaction that are transformed into products.

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Product Noun

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[prod-uhkt]

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Product

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A substance that is formed as the result of a chemical reaction, found on the right side of an equation.

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Example: In a chemical reaction, reactants like hydrogen (H₂) and oxygen (O₂) combine to form a new substance, which is called the product (water, H₂O).

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Mole Noun

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[mohl]

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Mole

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The SI unit for the amount of a substance, defined as containing exactly 6.022 x 10²³ elementary entities.

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Example: This diagram shows that one mole is a specific quantity of a substance, defined as the number of atoms in exactly 12 grams of carbon-12.

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Law of Conservation of Mass Noun

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[law uv kon-ser-vey-shuhn uv mas]

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Law of Conservation of Mass

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The principle that mass is neither created nor destroyed in a chemical reaction; total reactant mass equals total product mass.

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Example: In a closed container, the total mass of the chemicals before a reaction (184.34 g) is exactly equal to the total mass after the reaction, proving mass is conserved.

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Coefficient Noun

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[koh-uh-fish-uhnt]

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Coefficient

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A number placed before a chemical formula in a balanced equation indicating the relative number of moles of that substance.

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Example: The number '2' in front of O₂ and H₂O is a coefficient, showing that two molecules of oxygen react to produce two molecules of water.

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Avogadro's Number Noun

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[av-uh-gah-drohz nuhm-ber]

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Avogadro's Number

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The number of particles, such as atoms or molecules, in one mole of a substance, approximately 6.022 x 10²³.

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Example: The image defines Avogadro's number as the quantity in one mole (6.02 x 10^23) and shows how to use this value to convert moles of a substance into the number of atoms.

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Molar Mass Noun

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[moh-ler mas]

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Molar Mass

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The mass in grams of one mole of a substance, used as a conversion factor between mass and moles.

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Example: This image shows how to calculate the molar mass of a water molecule (H₂O) by adding the atomic masses of its two hydrogen atoms and one oxygen atom.

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Mole Ratio Noun

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[mohl rey-shee-oh]

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Mole Ratio

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A conversion factor from a balanced equation's coefficients that relates the moles of one substance to another.

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Example: The image visualizes a chemical reaction, showing that for every 2 sulfur atoms and 3 oxygen molecules used, 2 sulfur trioxide molecules are made.

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Dimensional Analysis Noun

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[di-men-shuh-nl uh-nal-uh-sis]

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Dimensional Analysis

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A problem-solving method that uses the cancellation of units to convert from an initial unit to a final desired unit.

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Example: This diagram shows how to convert units by multiplying a starting amount (24 inches) by a conversion factor (1 foot/12 inches), allowing the original units to cancel out.