Question

Write the equation for the reaction that corresponds to each of the following reaction quotients: (a) \(Q_{\mathrm{c}}=\frac{\left[\mathrm{H}_{2}\right]^{2}\left[\mathrm{~S}_{2}\right]}{\left[\mathrm{H}_{2} \mathrm{~S}\right]^{2}}\) (b) \(Q_{\mathrm{c}}=\frac{\left[\mathrm{NO}_{2}\right]^{2}\left[\mathrm{Cl}_{2}\right]}{\left[\mathrm{NClO}_{2}\right]^{2}}\) (c) \(Q_{\mathrm{c}}=\frac{\left[\mathrm{HgI}_{4}^{2-}\right]}{\left[\mathrm{Hg}^{2+}\right]\left[\mathrm{I}^{-}\right]^{4}}\) (d) \(Q_{\mathrm{c}}=\frac{[\mathrm{NO}]^{2}\left[\mathrm{Br}_{2}\right]}{[\mathrm{NOBr}]^{2}}\)

Short answer

(a) \(2\mathrm{H}_{2}\mathrm{S} \rightleftharpoons 2\mathrm{H}_{2} + \mathrm{S}_{2}\); (b) \(2\mathrm{NClO}_{2} \rightleftharpoons 2\mathrm{NO}_{2} + \mathrm{Cl}_{2}\); (c) \(\mathrm{Hg}^{2+} + 4\mathrm{I}^{-} \rightleftharpoons \mathrm{HgI}_{4}^{2-}\); (d) \(2\mathrm{NOBr} \rightleftharpoons 2\mathrm{NO} + \mathrm{Br}_{2}\).

Step-by-step solution

Identify the components in the reaction quotient for part (a)

For the reaction quotient \(Q_{c} = \frac{\left[\mathrm{H}_{2}\right]^{2}\left[\mathrm{~S}_{2}\right]}{\left[\mathrm{H}_{2}\mathrm{~S}\right]^{2}}\), identify which components are reactants and which are products. According to the general structure of reaction quotients, the terms in the numerator correspond to products and those in the denominator to reactants.

Write the chemical equation for part (a)

Since \(\left[\mathrm{H}_{2}\right]^{2}\left[\mathrm{~S}_{2}\right]\) are products and \(\left[\mathrm{H}_{2}\mathrm{~S}\right]^{2}\) are reactants, the balanced equation for part (a) is: \[ 2\mathrm{H}_{2}\mathrm{S} \rightleftharpoons 2\mathrm{H}_{2} + \mathrm{S}_{2} \].

Identify the components in the reaction quotient for part (b)

For the reaction quotient \(Q_{c} = \frac{\left[\mathrm{NO}_{2}\right]^{2}\left[\mathrm{Cl}_{2}\right]}{\left[\mathrm{NClO}_{2}\right]^{2}}\), identify which components are reactants and which are products. Products appear in the numerator and reactants appear in the denominator.

Write the chemical equation for part (b)

Since \(\left[\mathrm{NO}_{2}\right]^{2}\left[\mathrm{Cl}_{2}\right]\) are products and \(\left[\mathrm{NClO}_{2}\right]^{2}\) are reactants, the balanced equation is: \[ \mathrm{2NClO}_{2} \rightleftharpoons 2\mathrm{NO}_{2} + \mathrm{Cl}_{2} \].

Identify the components in the reaction quotient for part (c)

Look at \(Q_{c} = \frac{\left[\mathrm{HgI}_{4}^{2-}\right]}{\left[\mathrm{Hg}^{2+}\right]\left[\mathrm{I}^{-}\right]^{4}}\). The term in the numerator represent products and the terms in the denominator represent reactants.

Write the chemical equation for part (c)

The product \([\mathrm{HgI}_{4}^{2-}]\) and the reactants \([\mathrm{Hg}^{2+}]\) and \([\mathrm{I}^{-}]^{4}\) imply the equation \(\mathrm{Hg}^{2+} + 4\mathrm{I}^{-} \rightleftharpoons \mathrm{HgI}_{4}^{2-}\).

Identify the components in the reaction quotient for part (d)

Review the reaction quotient: \(Q_{c} = \frac{[\mathrm{NO}]^{2}\left[\mathrm{Br}_{2}\right]}{[\mathrm{NOBr}]^{2}}\). The numerator contains products and the denominator contains reactants.

Write the chemical equation for part (d)

Given \([\mathrm{NO}]^{2}\left[\mathrm{Br}_{2}\right]\) are products and \([\mathrm{NOBr}]^{2}\) are reactants, the chemical equation becomes: \(2\mathrm{NOBr} \rightleftharpoons 2\mathrm{NO} + \mathrm{Br}_{2}\).

Key concepts

Chemical Equilibrium

Chemical equilibrium is a fascinating state in a chemical reaction where the rate of the forward reaction equals the rate of the backward reaction. It's important to realize that at equilibrium, the concentrations of the reactants and products remain constant. However, this doesn't mean that the reactants and products are equal; it simply means that their concentrations remain stable over time.

Understanding equilibrium helps in predicting the quantity of each component in a reaction over time. When a system is at equilibrium, it experiences no net change. However, applying external conditions like temperature or pressure can shift the equilibrium, a concept known as Le Chatelier's principle.

Studying chemical equilibrium helps chemists control reactions, maximizing product yield, and ensuring reactions proceed safely and efficiently under controlled conditions.

Chemical Equation

A chemical equation is a symbolic representation of a chemical reaction. It shows the reactants on the left side and the products on the right side, with an arrow pointing from reactants to products. This arrow can be a single line for irreversible reactions or a double line, indicating reversibility and equilibrium.

Chemical equations must be balanced to respect the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a chemical reaction. Each element must have the same number of atoms on both sides of the equation. Balancing chemical equations involves adjusting the coefficients, which are the numbers placed before compounds or elements in the equation, without altering the chemical formulas.

Consider the equation: to represent the balanced state of a reaction, aids in understanding what happens during a chemical process. It emphasizes the principle that chemical changes involve rearrangements of atoms to form new substances.

Equilibrium Constant

The equilibrium constant, usually represented as is a numerical value that indicates the ratio of the concentrations of products to reactants at equilibrium. It is calculated using the equilibrium expression, which is derived from the balanced chemical equation.

For a general reaction if it's in equilibrium, It is essential to note that coefficients in a chemical equation become exponents in the equilibrium expression. The value of This implies that products predominate over reactants. Conversely, a low K value suggests reactants are favored. Understanding aids chemists in determining the direction in which a reaction proceeds under a given set of conditions. It's a pivotal concept when considering reaction spontaneity and extent.

Stoichiometry

Stoichiometry refers to the part of chemistry that deals with the calculation of reactants and products in chemical reactions. It's based on the conservation of mass and involves using balanced chemical equations to determine the quantities of substances.

By applying stoichiometry, we can predict how much product will form from given reactants or how much reactant is needed to produce a desired amount of product. Stoichiometry involves conversion factors based on mole ratios derived from a balanced chemical equation.

The process might be simplified into a few steps:

This helps chemists to understand reaction efficiencies and limitations, ultimately allowing for the optimal design of chemical processes.