A Model for Reaction Rates

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Reaction Rate Noun

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[ree-ak-shun rayt]

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Reaction Rate

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The speed at which a chemical reaction proceeds, measured as the change in concentration of a reactant or product over time.

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Example: This graph shows that as time passes, the starting chemicals (reagents) are used up, and new chemicals (products) are created, illustrating the progress of a reaction.

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Molar Concentration Noun

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[moh-ler kon-sen-tray-shun]

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Molar Concentration

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A quantitative measure of the amount of a substance (solute) dissolved in a given volume of solvent or solution.

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Example: This interactive diagram shows that molar concentration (molarity) depends on the amount of solute (drink mix) dissolved in a certain volume of solution.

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Collision Theory Noun

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[kuh-lizh-un thee-uh-ree]

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Collision Theory

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A model stating that for a reaction to occur, reactant particles must collide with the correct orientation and sufficient energy.

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Example: For a chemical reaction to happen, reactant particles must first collide with each other, as shown by the two spheres moving together and impacting.

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Activated Complex Noun

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[ak-tuh-vay-tid kom-pleks]

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Activated Complex

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A temporary, unstable arrangement of atoms formed at the peak of the activation energy barrier during a chemical reaction.

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Example: This graph shows that the activated complex is the temporary, high-energy state that reactants must pass through to become products in a chemical reaction.

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Activation Energy Noun

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[ak-tuh-vay-shun en-er-jee]

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Activation Energy

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The minimum amount of energy required for reacting particles to form the activated complex and initiate a chemical reaction.

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Example: This graph shows that activation energy is the minimum energy 'hill' that reactants must overcome to transform into products during a chemical reaction.

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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 its surroundings, resulting in products having lower energy than the reactants.

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Example: Burning wood is a combustion reaction, a type of exothermic reaction where fuel (hydrocarbon) and oxygen create heat, light, carbon dioxide, and water.

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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, resulting in products having higher energy than the reactants.

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Example: Energy, shown by the arrows, is absorbed from the surroundings into the test tube to fuel the chemical reaction.

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Spontaneous Reaction Noun

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[spon-tay-nee-uhs ree-ak-shun]

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Spontaneous Reaction

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A reaction that is thermodynamically favored to occur without external energy input, though its rate can be fast or slow.

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Example: Mixing hydrochloric acid with iron powder causes a chemical reaction that produces gas bubbles, demonstrating a reaction that proceeds on its own without continuous energy.