Describe the nature of equilibrium systemsExplain the dynamic nature the a chemical equilibrium

The convention for creating chemical equations involves placing reactant recipe on the left side of a reaction arrow and product recipe on the ideal side. Through this convention, and also the meanings of “reactant” and also “product,” a chemistry equation to represent the reaction in concern as proceeding indigenous left come right. Reversible reactions, however, may proceed in both front (left come right) and reverse (right come left) directions. As soon as the rates of the forward and reverse reactions room equal, the concentration of the reactant and also product varieties remain consistent over time and also the mechanism is at equilibrium. The relative concentrations the reactants and products in equilibrium solution vary greatly; some solution contain mostly products at equilibrium, part contain greatly reactants, and also some save appreciable quantities of both.

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(Figure) illustrates basic equilibrium concepts using the reversible decomposition of colorless dinitrogen tetroxide to yield brown nitrogen dioxide, an elementary reaction defined by the equation:


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As the reaction begins (t = 0), the concentration that the N2O4 reactant is finite and also that that the NO2 product is zero, for this reason the front reaction proceeds at a finite price while the reverse reaction price is zero. Together time passes, N−2O4 is consumed and also its concentration falls, when NO2 is produced and also its concentration rises ((Figure)b). The diminish concentration that the reactant slows the forward reaction rate, and the increasing product concentration speeds the reverse reaction price ((Figure)c). This process continues until the forward and also reverse reaction rates come to be equal, at which time the reaction has reached equilibrium, as identified by consistent concentrations of its reactants and products (shaded locations of (Figure)b and also (Figure)c). It’s essential to emphasize the chemical equilibria room dynamic; a reaction in ~ equilibrium has not “stopped,” however is proceeding in the forward and also reverse direction at the exact same rate. This dynamic nature is important to expertise equilibrium behavior as disputed in this and also subsequent chapters the the text.


A two-person juggling plot illustrates the dynamic aspect of chemical equilibria. Each human being is throwing and catching clubs in ~ the exact same rate, and each hold a (approximately) constant number of clubs.

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Physical changes, such together phase transitions, are also reversible and may establish equilibria. This ide was presented in another chapter the this message through conversation of the vapor press of a condensed phase (liquid or solid). Together one example, consider the vaporization the bromine:


When liquid bromine is included to an otherwise north container and the container is sealed, the forward procedure depicted over (vaporization) will commence and also continue in ~ a roughly continuous rate as long as the exposed surface area of the liquid and its temperature remain constant. Together increasing amounts of gas bromine are produced, the price of the reverse process (condensation) will rise until it amounts to the price of vaporization and equilibrium is established. A picture showing this phase transition equilibrium is provided in (Figure).

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A sealed tube containing one equilibrium mixture the liquid and gaseous bromine. (credit: http://images-of-elements.com/bromine.php)

Key Concepts and also Summary

A reversible reaction is at equilibrium once the forward and reverse processes occur at equal rates. Chemical equilibria space dynamic processes identified by consistent amounts the reactant and also product species.