Reactions

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Substance Noun

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[sub-stans]

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Substance

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A form of matter with a uniform and definite composition, made of a single type of atom or molecule.

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Example: This image shows different types of pure substances, including elements like tin and compounds like water, which all have a uniform composition.

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Property Noun

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[prop-er-tee]

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Property

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A characteristic of a substance that can be observed or measured and is used for its identification.

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Example: This gold is yellow, shiny, and solid. These observable characteristics are its physical properties.

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Atom Noun

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[at-uhm]

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Atom

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The basic unit of a chemical element and the fundamental building block of all substances and matter.

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Example: This diagram shows an atom's structure: a central nucleus with protons and neutrons, and electrons orbiting the nucleus in distinct energy shells.

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Molecule Noun

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[mol-uh-kyool]

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Molecule

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A group of two or more atoms held together by chemical bonds, forming a substance's smallest chemical unit.

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Example: This image shows a carbon dioxide (CO₂) molecule, where one carbon atom is chemically bonded to two oxygen atoms, forming a single unit.

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Chemical Reaction Noun

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

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Chemical Reaction

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A process where substances are converted into different substances by rearranging the atoms that compose them.

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Example: Hydrogen and oxygen molecules (reactants) rearrange their atoms to form new water molecules (products), shown by the chemical equation and models.

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Reactant Noun

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[ree-ak-tuhnt]

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Reactant

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A starting substance that participates in and undergoes change during the course of a chemical reaction.

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Example: The molecules on the left (CH₄ and O₂), labeled REACTANTS, are the starting materials that will combine and change in the chemical reaction.

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Product Noun

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[prod-uhkt]

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Product

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A new substance that is formed as the result of a chemical reaction between one or more reactants.

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Example: In a chemical reaction, the new substances that are formed, like water (H₂O) in this diagram, are called the products.

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Conserved Adjective

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[kuhn-survd]

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Conserved

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Describing a quantity that remains constant throughout a process, such as mass during a chemical reaction.

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Example: A balanced scale represents conservation, showing that the total amount of something, like mass, remains equal before and after a change.

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Model Noun

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[mod-l]

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Model

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A representation used to study and explain ideas, objects, or processes that are too difficult to observe directly.

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Example: This Bohr model is a simplified diagram of a sodium atom, showing the arrangement of electrons in shells, helping us visualize something too small to see.

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Endothermic Reaction Noun

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[en-doh-thur-mik ree-ak-shun]

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Endothermic Reaction

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A chemical reaction that absorbs energy from its surroundings, often causing a noticeable decrease in temperature.

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Example: This icon shows a chemical reaction in a test tube absorbing energy from its surroundings, as represented by the arrows pointing inward.