Reactions and Equations

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Chemical Reaction Noun

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[kem-i-kuhl ree-ak-shun]

Back

Chemical Reaction

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The process by which the atoms of one or more substances are rearranged to form entirely different substances.

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Example: This diagram shows how starting substances (reactants) like methane and oxygen break their bonds and rearrange their atoms to form new substances (products) like carbon dioxide and water.

Front

Reactants Noun

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[ree-ak-tants]

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Reactants

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The starting substances in a chemical reaction, which are written to the left of the arrow in a chemical equation.

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Example: The starting substances in a chemical reaction, like methane (CH₄) and oxygen (O₂), are called reactants. They are shown on the left of the arrow.

Front

Products Noun

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[prod-ukts]

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Products

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The new substances formed during a chemical reaction, which are written to the right of the arrow in an equation.

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Example: In a chemical reaction, reactants like methane and oxygen rearrange their atoms to form new substances called products, such as carbon dioxide and water.

Front

Chemical Equation Noun

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[kem-i-kuhl ee-kway-zhun]

Back

Chemical Equation

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A statement using chemical formulas to show the identities and relative amounts of the substances in a chemical reaction.

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Example: This diagram shows a chemical equation where two hydrogen molecules (2H₂) and one oxygen molecule (O₂) react to form two water molecules (2H₂O).

Front

Aqueous Adjective

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[ey-kwee-uhs]

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Aqueous

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A term describing a substance that has been dissolved in water, identified by the symbol (aq) in an equation.

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Example: This diagram shows how a solid ionic compound dissolves in water. The water molecules pull apart the positive and negative ions, creating an aqueous solution.

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Word Equation Noun

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[wurd ee-kway-zhun]

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Word Equation

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An equation that uses the names of substances, rather than chemical formulas, to indicate the reactants and products.

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Example: This image shows a word equation for photosynthesis, where reactants like carbon dioxide and water are written as words to show they form products.

Front

Skeleton Equation Noun

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[skel-i-tn ee-kway-zhun]

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Skeleton Equation

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An equation using chemical formulas to identify reactants and products but not indicating the relative amounts of each.

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Example: This image shows a balanced chemical equation where atoms are conserved, but a skeleton equation is an initial, unbalanced version of the reaction.

Front

Law of Conservation of Mass Noun

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

Back

Law of Conservation of Mass

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The fundamental law stating that in a chemical change, matter is neither created nor destroyed, only rearranged.

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Example: This diagram shows a chemical reaction where the number of atoms for each element (carbon, hydrogen, oxygen) is the same in the reactants and products.

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Coefficient Noun

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[koh-uh-fish-uhnt]

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Coefficient

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The number written in front of a reactant or product that specifies the relative amount of that substance.

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Example: The coefficient, like the '2' before O₂, is a number in a chemical equation that shows how many molecules are involved in the reaction.

Front

Balanced Chemical Equation Noun

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[bal-uhnsd kem-i-kuhl ee-kway-zhun]

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Balanced Chemical Equation

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A chemical equation in which the number of atoms of each element is equal on both the reactant and product sides.

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Example: This experiment shows that when reactants are mixed in a closed system, the total mass does not change, demonstrating the principle of a balanced chemical equation.