Types of Chemical Reactions

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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 that involves the rearrangement of atoms in one or more substances to form new, different chemical substances.

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Example: This diagram shows reactants (methane and oxygen) on the left rearranging their atoms to form new products (carbon dioxide and water) on the right.

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Precipitate Noun

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[prih-sip-i-teyt]

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Precipitate

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An insoluble solid that emerges from a liquid solution during a chemical reaction, often appearing as a cloudy suspension.

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Example: When two solutions are mixed, a chemical reaction can form an insoluble solid called a precipitate, which then settles to the bottom of the liquid.

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Exothermic Reaction Noun

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[ek-soh-thur-mik ree-ak-shun]

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Exothermic Reaction

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A chemical reaction that releases energy into the surroundings, typically in the form of heat, causing a temperature increase.

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Example: An exothermic reaction releases energy, usually as heat, causing the surroundings to become hotter. The arrows show heat moving out from the reaction.

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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, usually as heat, causing a noticeable drop in temperature.

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Example: This diagram shows the inside of an instant cold pack, where dissolving ammonium nitrate in water is an endothermic reaction that absorbs heat.

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Synthesis Reaction Noun

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[sin-thuh-sis ree-ak-shun]

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Synthesis Reaction

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A type of chemical reaction in which two or more simple substances combine to form a single, more complex product.

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Example: Two simple substances, hydrogen (H₂) and oxygen (O₂), combine to form a more complex substance, water (H₂O), which is a synthesis reaction.

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Decomposition Reaction Noun

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[dee-kom-puh-zish-un ree-ak-shun]

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Decomposition Reaction

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A type of chemical reaction where a single compound breaks down into two or more simpler elements or new compounds.

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Example: Using electricity, a single compound (water) is broken down into two simpler substances (hydrogen gas and oxygen gas), a process called electrolysis.

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Single Replacement Reaction Noun

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[sing-guhl ri-pleys-muhnt ree-ak-shun]

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Single Replacement Reaction

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A chemical reaction where an element reacts with a compound, displacing another element to form a new element and compound.

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Example: This diagram shows a single element 'A' replacing another element 'B' in a compound 'BC', resulting in a new element 'B' and a new compound 'AC'.

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Double Replacement Reaction Noun

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[duhb-uhl ri-pleys-muhnt ree-ak-shun]

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Double Replacement Reaction

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A chemical reaction where the positive and negative ions of two ionic compounds exchange places to form two new compounds.

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Example: Two clear liquid compounds (CaCl₂ and Na₂SO₄) are mixed, causing their ions to switch partners and form a solid precipitate (CaSO₄).

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Combustion Reaction Noun

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[kuhm-buhs-chun ree-ak-shun]

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Combustion Reaction

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A rapid reaction between a hydrocarbon and oxygen that releases heat and light, producing carbon dioxide and water as products.

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Example: This diagram shows the inputs and outputs of a combustion reaction: a hydrocarbon (like charcoal) plus oxygen creates carbon dioxide, water, and energy (heat and light).

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Hydrocarbon Noun

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[hahy-droh-kahr-buhn]

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Hydrocarbon

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An organic compound consisting entirely of hydrogen and carbon atoms, commonly found in fossil fuels and used in combustion.

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Example: This image shows a model of a methane molecule (CH₄), the simplest example of a hydrocarbon, which is a compound made of hydrogen and carbon atoms.