Percent Yield

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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 study and calculation of quantitative relationships between the amounts of reactants used and products formed in a chemical reaction.

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Example: This diagram shows the relationship between atoms, moles, and mass, which are foundational calculations used in stoichiometry to determine theoretical yield.

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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 any two substances in the reaction.

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Example: This balanced chemical equation shows that 1 molecule of methane reacts with 2 molecules of oxygen, establishing a 1:2 mole ratio between them.

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Limiting Reactant Noun

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[lim-it-ing ree-ak-tant]

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Limiting Reactant

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The reactant that is completely consumed in a reaction, thereby determining the maximum amount of product that can be formed.

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Example: This diagram shows a chemical reaction where the green chlorine (Cl₂) molecules are completely used up, making them the limiting reactant, while some white hydrogen (H₂) molecules are left over.

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Excess Reactant Noun

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[ek-ses ree-ak-tant]

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Excess Reactant

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A reactant that remains after the limiting reactant is completely used up in a chemical reaction.

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Example: In a reaction between H₂ (white) and Cl₂ (green) molecules, all the Cl₂ is used up, but some H₂ is left over, making it the excess reactant.

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Theoretical Yield Noun

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[thee-uh-ret-i-kuhl yeeld]

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Theoretical Yield

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The maximum amount of product that can be produced from a given amount of reactant, as calculated from stoichiometry.

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Example: This image shows the perfect 'recipe' for a chemical reaction. Theoretical yield is the maximum amount of product calculated from this ideal recipe.

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Percent Yield Noun

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[per-sent yeeld]

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Percent Yield

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The ratio of the actual yield to the theoretical yield, expressed as a percentage, which measures a reaction's efficiency.

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Example: This image shows the formula for percent yield, which compares the actual amount of product made in a reaction to the maximum theoretical amount possible.

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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 in an isolated system is neither created nor destroyed by chemical reactions or physical transformations.

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Example: In a chemical reaction, atoms are rearranged, not created or destroyed. The total mass of reactants equals the total mass of the products.

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Competing Reactions Noun

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[kuhm-peet-ing ree-ak-shuhns]

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Competing Reactions

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Side reactions that occur along with the main reaction, forming unintended products and reducing the yield of the desired product.

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Example: A single set of starting chemicals (reactants) can sometimes react in different ways, creating two or more different resulting chemicals (products).

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Catalyst Noun

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[kat-l-ist]

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Catalyst

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A substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.

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Example: A catalytic converter in a car uses a catalyst to change harmful engine emissions (reactants) into less harmful substances (products) like water and CO2.