Defining Stoichiometry

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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 of quantitative relationships between the amounts of reactants used and products formed by a chemical reaction.

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Example: A balanced chemical reaction shows atoms rearranging from reactants (left) to products (right). The number of each type of atom remains the same.

Front

Reactant Noun

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[ree-ak-tant]

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Reactant

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A starting substance in a chemical reaction that is consumed during the process and written on the left side of a chemical equation.

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Example: The image shows a chemical reaction where the starting substances on the left, methane (CH4) and oxygen (O2), are the reactants.

Front

Product Noun

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[prod-ukt]

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Product

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A substance formed as the result of a chemical reaction, written on the right side of the arrow in a chemical equation.

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Example: In a chemical reaction, reactants like hydrogen (H₂) and oxygen (O₂) combine to form new substances, called products, such as water (H₂O).

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Law of Conservation of Mass Noun

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

Back

Law of Conservation of Mass

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The principle stating that matter is not created or destroyed in a chemical reaction, so the mass of reactants equals the mass of products.

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Example: This image shows that in a chemical reaction, atoms are rearranged, not created or destroyed. The same number of each type of atom exists before and after.

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Representative Particle Noun

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[rep-ri-zen-tuh-tiv par-ti-kuhl]

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Representative Particle

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The smallest unit of a substance, which can be an atom, molecule, or formula unit, depending on the substance's chemical nature.

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Example: A water molecule is a representative particle for the compound water; it's the smallest unit that is still identifiable as water.

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

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Example: The image shows that the coefficient '2' in a chemical equation means there are two molecules of that substance, like the two O₂ molecules.

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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 any pure substance, used as a conversion factor between mass and moles.

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Example: This image shows that molar mass is the mass (measured on the scale) of one mole of a substance (represented by the cartoon mole).

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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 ratio between the numbers of moles of any two substances in a balanced chemical equation, derived from the equation's coefficients.

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Example: This diagram shows that two hydrogen molecules react with one oxygen molecule to create two water molecules, illustrating the 2:1:2 mole ratio.

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Formula Unit Noun

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[fawr-myuh-luh yoo-nit]

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Formula Unit

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The simplest whole-number ratio of ions in an ionic compound, which serves as the representative particle for that compound.

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Example: This image shows one sodium ion (Na+) and one chloride ion (Cl-), representing the simplest whole-number ratio (1:1) for the ionic compound sodium chloride.