Le Chatelier’s Principle

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Reversible Reaction Noun

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

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Reversible Reaction

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A chemical reaction that can proceed in both the forward and backward directions, from reactants to products and vice versa.

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Example: This image compares an open glass (irreversible evaporation) to a sealed glass, where water evaporates and condenses back, showing a reversible reaction at equilibrium.

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Dynamic Equilibrium Noun

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

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Dynamic Equilibrium

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The state where forward and reverse reaction rates are equal, resulting in constant reactant and product concentrations in a closed system.

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Example: This image shows a dog pulling forward while its owner pulls back with equal force. This represents dynamic equilibrium, where opposing actions happen at the same rate, resulting in no overall change.

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Closed System Noun

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[klohzd sis-tuhm]

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Closed System

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A physical system where no matter or energy can enter or leave, which is a necessary condition for achieving equilibrium.

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Example: This diagram shows a closed system, where energy like heat can get out, but matter cannot, which is necessary for Le Chatelier's principle.

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Le Chatelier's Principle Noun

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[luh sha-tel-yayz prin-suh-puhl]

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Le Chatelier's Principle

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The principle that if a change is applied to a system at equilibrium, the system will shift to counteract that change.

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Example: This analogy shows a system at equilibrium (equal water levels) being stressed (more water added). The system responds by shifting to relieve the stress, reaching a new equilibrium.

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Equilibrium Shift Noun

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[ee-kwuh-lib-ree-um shift]

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Equilibrium Shift

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The change in the position of equilibrium, either favoring reactants or products, in response to an external stress on the system.

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Example: This diagram shows that in a reversible chemical reaction, adding a substance (reactant) causes the reaction to shift away from it, toward the products.

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Equilibrium Constant Noun

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

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Equilibrium Constant

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A value expressing the ratio of product to reactant concentrations at equilibrium, which is constant for a given temperature.

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Example: This image shows the mathematical formula for the Equilibrium Constant (Kc), which is the ratio of product concentrations to reactant concentrations in a reaction.

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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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The reaction in a reversible process where the initial reactants are converted into products, proceeding from left to right.

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Example: This diagram shows reactants (hydrogen and oxygen molecules) on the left turning into a product (water molecules) on the right, indicated by the forward-pointing arrow.

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Backward Reaction Noun

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[bak-werd ree-ak-shun]

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Backward Reaction

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The reaction in a reversible process where the products are converted back into the original reactants, proceeding from right to left.

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Example: In a closed container, water evaporates (forward reaction) and also condenses back into liquid (backward reaction), creating a balance called equilibrium.

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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, usually as heat, into its surroundings and has a negative enthalpy change (ΔH).

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Example: This diagram shows an exothermic reaction releasing heat outwards, making the area around it hotter than its surroundings, a key concept for Le Chatelier's Principle.

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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, usually as heat, from its surroundings and has a positive enthalpy change (ΔH).

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Example: The arrows pointing into the test tube show that the chemical reaction inside is absorbing energy, like heat, from its surroundings.