Consider the reaction:
NH4HS(s)ΔNH3( g) + H2S( g)
At a certain temperature, Kc = 8.5 * 10 - 3. A reaction mixture at this temperature containing solid NH4HS has [NH3] = 0.0822 M and [H2S] = 0.0822M. Will more of the solid form, or will some of the existing solid decompose as equilibrium is reached?

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insert step 1> Identify the reaction and the equilibrium constant expression. The reaction is NH4HS(s) ⇌ NH3(g) + H2S(g). The equilibrium constant expression for this reaction is K_c = [NH3][H2S].

insert step 2> Substitute the given concentrations into the equilibrium expression. You have [NH3] = 0.0822 M and [H2S] = 0.0822 M.

insert step 3> Calculate the reaction quotient, Q_c, using the initial concentrations: Q_c = [NH3][H2S] = (0.0822)(0.0822).

insert step 4> Compare the calculated Q_c with the given K_c (8.5 * 10^-3).

insert step 5> Determine the direction of the reaction: If Q_c < K_c, the reaction will proceed to the right, decomposing more solid NH4HS. If Q_c > K_c, the reaction will proceed to the left, forming more solid NH4HS.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In this state, the system is dynamic, meaning that reactions continue to occur, but there is no net change in the concentrations. Understanding equilibrium is crucial for predicting how changes in conditions (like concentration or temperature) will affect the position of the equilibrium.

Equilibrium Constant (Kc)

The equilibrium constant (Kc) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium, each raised to the power of their coefficients in the balanced equation. For the given reaction, Kc = [NH3][H2S] / [NH4HS]. A small Kc value, like 8.5 x 10^-3, indicates that at equilibrium, the concentration of reactants is much higher than that of products, suggesting that the reaction favors the formation of reactants.

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust to counteract that change and restore a new equilibrium. In the context of the given reaction, if the concentration of NH3 and H2S increases, the system may shift to favor the formation of solid NH4HS, while a decrease in these concentrations could lead to more solid decomposing into gases.

Consider the reaction:NH4HS(s)ΔNH3( g) + H2S( g)At a certain temperature, Kc = 8.5 * 10 - 3. A reaction mixture at this temperature containing solid NH4HS has [NH3] = 0.0822 M and [H2S] = 0.0822M. Will more of the solid form, or will some of the existing solid decompose as equilibrium is reached?

Verified video answer for a similar problem:

Key Concepts

Chemical Equilibrium

Equilibrium Constant (Kc)

Le Chatelier's Principle