Show that the complete chemical equation, the total ionic equation, and the net ionic equation for the reaction represented by the equation \(\mathrm{KI}(a q)+\mathrm{I}_{2}(a q) \rightleftharpoons \mathrm{KI}_{3}(a q)\) give the same expression for the reaction quotient. \(\mathrm{KI}_{3}\) is composed of the ions \(K^{+}\) and \(I_{3}^{-}\)

Understanding the chemical equation involves recognizing how substances react to form new substances. Chemical equations provide a succinct way to represent these reactions. Each chemical equation consists of reactants (substances that start the reaction) and products (substances that are produced by the reaction). For educational clarity, let's consider the provided equation:
In the exercise, the balanced chemical equation is \[\begin{equation}\mathrm{KI}(aq) + \mathrm{I}_{2}(aq) \rightleftharpoons \mathrm{KI}_{3}(aq)\end{equation}\]which shows potassium iodide reacting with iodine to form triiodide. This equation communicates not only the substances involved but also their states; in this case, 'aq' denotes that the substances are aqueous, or dissolved in water. It's important for students to acknowledge that the law of conservation of mass is upheld in chemical equations: the number of atoms of each element is the same on both sides of the reaction.

The reaction quotient () is a measure of the relative amounts of products and reactants present during a chemical reaction at a given moment. It is calculated similarly to the equilibrium constant, but for a reaction that has not necessarily reached equilibrium. \[\begin{equation}Q = \frac{[Products]}{[Reactants]}\end{equation}\]In the context of the given exercise, for the complete chemical equation, total ionic equation, and net ionic equation is used to show the state of the reaction. When equals the equilibrium constant (), the reaction is at equilibrium and no net change occurs in the concentration of reactants and products. By demonstrating that all expressions for are equivalent, it illustrates the consistency of the reaction's progress, regardless of how the reaction is represented.

The total ionic equation provides an in-depth view of the chemical reaction by showing all the ions present when the reactants are dissolved in aqueous solutions. This representation is vital for understanding reactions in an ionic context. For the given exercise, the total ionic equation is:\[\begin{equation}K^{+}(aq) + I^{-}(aq) + \mathrm{I}_{2}(aq) \rightleftharpoons K^{+}(aq) + I_{3}^{-}(aq)\end{equation}\]This equation demonstrates the reaction on an ionic level, highlighting which compounds dissociate into ions in solution. It’s an intermediate step between the complete chemical equation and the net ionic equation, helping students grasp the reaction's nuance.

Spectator ions are ions that do not change during the course of a reaction; they appear unchanged on both the reactant and the product sides of a chemical equation. These ions are not directly involved in the formation of the product and are therefore 'spectators' to the reaction. In our example, the potassium ion () is a spectator ion, as it remains unchanged from the reactants to the products:\[\begin{equation}K^{+}(aq) \text{ (reactants) } \rightarrow K^{+}(aq) \text{ (products) }\end{equation}\]Identifying and eliminating spectator ions when transitioning from the total ionic equation to the net ionic equation simplifies the reaction and focuses on the species that actually undergo chemical change.

Chemical equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction, and the concentrations of reactants and products remain unchanged over time. It's a dynamic state where reactions continue to occur, but without net change in concentration of reactants and products. This concept is significant when discussing reversible reactions, such as the one in the exercise:\[\begin{equation}\mathrm{KI}(aq) + \mathrm{I}_{2}(aq) \rightleftharpoons \mathrm{KI}_{3}(aq)\end{equation}\]At equilibrium, the reaction quotient () equals the equilibrium constant (), signifying no further change in the system. Understanding equilibrium is fundamental in predicting how the system will respond to changes, as outlined by Le Chatelier's principle, making it a key concept in chemistry.