Chemical Equilibrium

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Reversible Reaction Noun

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[ri-vur-suh-buhl ree-ak-shun]

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Reversible Reaction

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A chemical reaction where products can react to re-form reactants, proceeding in both forward and reverse directions.

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Example: This image shows that in a closed glass, water evaporates and condenses back into liquid. This is a reversible process, unlike the open glass where water only evaporates away.

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Chemical Equilibrium Noun

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[kem-i-kuhl ee-kwuh-lib-ree-uhm]

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Chemical Equilibrium

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The state where forward and reverse reaction rates are equal, resulting in constant concentrations of reactants and products.

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Example: This graph shows that in a reversible reaction, equilibrium is reached when the concentrations of reactants (N₂O₄) and products (NO₂) stop changing over time.

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Equilibrium Constant (K) Noun

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[ee-kwuh-lib-ree-uhm kon-stuhnt]

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Equilibrium Constant (K)

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A value representing the ratio of product concentrations to reactant concentrations at equilibrium, each raised to its stoichiometric coefficient.

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Example: This image shows the math formula for the equilibrium constant (Kc), which compares the amount of products to the amount of reactants in a reversible chemical reaction.

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Homogeneous Equilibrium Noun

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[hoh-muh-jee-nee-uhs ee-kwuh-lib-ree-uhm]

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Homogeneous Equilibrium

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A chemical equilibrium in which all reactants and products are in the same physical phase, such as all gaseous.

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Example: This image shows two reversible chemical reactions where all substances—both reactants and products—are in the same gas phase, indicated by the symbol (g).

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Heterogeneous Equilibrium Noun

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[het-er-uh-jee-nee-uhs ee-kwuh-lib-ree-uhm]

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Heterogeneous Equilibrium

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A chemical equilibrium in which the reactants and products are present in more than one physical phase.

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Example: This diagram shows a chemical reaction at equilibrium inside a beaker where the substances are in different physical states (phases), like a solid at the bottom and dissolved particles in the liquid.

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Dynamic Equilibrium Noun

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[dy-nam-ik ee-kwuh-lib-ree-uhm]

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Dynamic Equilibrium

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An equilibrium state where forward and reverse reactions continue at equal rates, resulting in no net change in the system.

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Example: A dog running on a leash but staying in place shows dynamic equilibrium, where forward and reverse actions happen at the same rate.

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Law of Mass Action Noun

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[law uv mas ak-shun]

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Law of Mass Action

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The principle that a reaction's rate is proportional to the product of reactant concentrations, forming the basis for equilibrium expressions.

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Example: This image shows a calculation for the equilibrium constant (K), a mathematical application of the Law of Mass Action for a specific chemical reaction.

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Reaction Quotient (Q) Noun

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[ree-ak-shun kwoh-shunt]

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Reaction Quotient (Q)

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A value calculated from reactant and product concentrations at any point, used to predict the direction of a reaction shift.

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Example: This diagram shows that when the reaction quotient (Q) is less than the equilibrium constant (K), the reaction shifts to make more products (B).

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Forward Reaction Noun

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[for-werd ree-ak-shun]

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Forward Reaction

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In a reversible process, the reaction that converts reactants into products as written from left to right in an equation.

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Example: Reactants like methane (CH4) and oxygen (O2) combine and change into new products like carbon dioxide (CO2) and water (H2O).

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Reverse Reaction Noun

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[ri-vurs ree-ak-shun]

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Reverse Reaction

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In a reversible process, the reaction that converts products back into reactants as written from right to left in an equation.

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Example: This image compares an open glass, where water evaporates away, to a closed glass, where water both evaporates (forward reaction) and condenses (reverse reaction).