Potential Energy Diagrams

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Potential Energy Noun

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[po-ten-shul en-er-jee]

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Potential Energy

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The energy stored within a chemical substance based on its composition and the arrangement of its atoms.

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Example: This diagram compares three scenarios to show how an object's gravitational potential energy increases with greater mass and height above a reference point.

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Reactants Noun

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[ree-ak-tants]

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Reactants

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The initial substances that enter into and are altered during a chemical reaction, shown on the left of an equation.

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Example: This diagram shows that reactants (A and B) are the starting substances in a chemical reaction that combine and rearrange to form new products.

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Products Noun

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[prod-ukts]

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Products

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The new substances that are formed as a result of a chemical reaction, shown on the right of an equation.

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Example: This diagram shows that products (C and D) are the new substances formed after the starting materials, called reactants (A and B), have chemically changed.

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Reaction Coordinate Noun

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[ree-ak-shun kor-di-nit]

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Reaction Coordinate

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The axis on a potential energy diagram that represents the progress of a reaction from reactants to products.

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Example: This diagram shows the energy of a chemical reaction as it progresses. The horizontal axis, or 'reaction coordinate,' tracks the path from starting reactants to products.

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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, high-energy arrangement of atoms that exists at the peak of the activation energy barrier during a reaction.

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Example: This diagram shows that the activated complex is the temporary, high-energy state at the very top of the energy 'hill' that reactants must overcome to become products.

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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 reactants to transform into the activated complex and initiate a chemical reaction.

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Example: This graph shows a reaction needs a 'push' of energy to start, called activation energy. An enzyme makes this push, or energy hill, smaller.

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Enthalpy (ΔH) Noun

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[en-thal-pee / del-tuh aych]

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Enthalpy (ΔH)

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The overall change in heat content of a system during a chemical reaction, also known as the heat of reaction.

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Example: This diagram shows an endothermic reaction where products have more enthalpy (energy) than reactants, resulting in a positive change in enthalpy (+ΔH).

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Endothermic Adjective

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[en-doh-thur-mik]

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Endothermic

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Describes a chemical process that absorbs heat energy from its surroundings, resulting in a positive change in enthalpy (ΔH).

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Example: An endothermic process is shown by a beaker absorbing heat from the surroundings, illustrated by arrows pointing inward, causing the system's contents to feel cold.

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Exothermic Adjective

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[ek-soh-thur-mik]

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Exothermic

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Describes a chemical process that releases heat energy into its surroundings, resulting in a negative change in enthalpy (ΔH).

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Example: This potential energy diagram shows an exothermic reaction, where the products have less energy than the reactants, meaning energy has been released.

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Catalyst Noun

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[kat-uh-list]

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Catalyst

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A substance that increases the rate of a chemical reaction by providing an alternative pathway with lower activation energy.

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Example: This potential energy diagram shows that a catalyst (red path) provides a shortcut for a chemical reaction, lowering the 'energy hill' (activation energy) needed to go from reactants to products.