Question

Write the Keq expression for each reaction. a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O} \mathrm{H}+\mathrm{NaI} \rightleftarrows \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I}+\mathrm{NaOH}\) b) \(\mathrm{PCl}_{3}+\mathrm{Cl}_{2} \rightleftarrows \mathrm{PCl}_{5}\)

Short answer

a) \( K_{eq} = \frac{[\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I}][\mathrm{NaOH}]}{[\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O} \mathrm{H}][\mathrm{NaI}]} \); b) \( K_{eq} = \frac{[\mathrm{PCl}_{5}]}{[\mathrm{PCl}_{3}][\mathrm{Cl}_{2}]} \)."

Step-by-step solution

Understand the Reaction

Before writing the equilibrium constant expression, understand that the equilibrium constant (\( K_{eq} \)) of a chemical reaction in terms of concentration can be expressed as a fraction with products in the numerator and reactants in the denominator.

Identify the Reaction Components (Part a)

For the reaction \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O} \mathrm{H} + \mathrm{NaI} \rightleftarrows \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I} + \mathrm{NaOH} \), identify the products and reactants. Reactants: \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O} \mathrm{H} \) and \( \mathrm{NaI} \); Products: \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I} \) and \( \mathrm{NaOH} \).

Write the Keq Expression (Part a)

Use the concentrations of products and reactants to write the expression for equilibrium constant (\( K_eq \)) for part (a):\[ K_{eq} = \frac{[\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I}][\mathrm{NaOH}]}{[\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O} \mathrm{H}][\mathrm{NaI}]} \]

Identify the Reaction Components (Part b)

For the reaction \( \mathrm{PCl}_{3} + \mathrm{Cl}_{2} \rightleftarrows \mathrm{PCl}_{5} \), identify the products and reactants. Reactants: \( \mathrm{PCl}_{3} \) and \( \mathrm{Cl}_{2} \); Product: \( \mathrm{PCl}_{5} \).

Write the Keq Expression (Part b)

Write the expression for the equilibrium constant (\( K_eq \)) for part (b):\[ K_{eq} = \frac{[\mathrm{PCl}_{5}]}{[\mathrm{PCl}_{3}][\mathrm{Cl}_{2}]} \]

Key concepts

Equilibrium Constant

The equilibrium constant, denoted as \( K_{eq} \), is vital in understanding how a chemical reaction behaves at equilibrium. It tells us the ratio of the concentration of products to reactants when a reaction has reached its balanced state, meaning that the rates of the forward and reverse reactions are equal. The equilibrium constant expression is written by placing the concentrations of the products in the numerator and the concentrations of the reactants in the denominator. The concentrations are usually represented in moles per liter (M). When calculating \( K_{eq} \), it's important to:

• Write concentrations of products on the top and reactants at the bottom.
• Use powers that correspond to the coefficients in the balanced chemical equation.

A \( K_{eq} \) value much greater than 1 implies a predominance of products, whereas a \( K_{eq} \) less than 1 indicates more reactants at equilibrium.

Chemical Reactions

Chemical reactions describe processes where reactants are transformed into products. They can be influenced by temperature, pressure, and concentration of reactants, among other factors. In a balanced chemical reaction, the number of atoms of each element is equal on both sides of the equation, ensuring the conservation of mass. An example is the reaction between ethanol and sodium iodide:

• Reactants interact in a dynamic process, leading to the formation of new products.
• This dynamic process can reach equilibrium, where the composition doesn't change over time.

Knowing the reactants and products helps define the path and speed of the reaction, aiding in understanding the overall chemical process.

Reactant and Product Identification

Identifying reactants and products in a chemical reaction is crucial for writing equilibrium expressions. Reactants are the substances that undergo change, while products are the new substances formed.For the reaction \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} + \mathrm{NaI} \rightleftarrows \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I} + \mathrm{NaOH} \):

• The reactants are ethanol (\( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} \)) and sodium iodide (\( \mathrm{NaI} \)).
• The products formed are ethyl iodide (\( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I} \)) and sodium hydroxide (\( \mathrm{NaOH} \)).

In another example, \( \mathrm{PCl}_{3} + \mathrm{Cl}_{2} \rightleftarrows \mathrm{PCl}_{5} \):

• Here, phosphorus trichloride (\( \mathrm{PCl}_{3} \)) and chlorine (\( \mathrm{Cl}_{2} \)) are the reactants.
• Phosphorus pentachloride (\( \mathrm{PCl}_{5} \)) is the product.

Identifying these correctly allows you to construct a valid equilibrium expression, which is crucial for understanding reaction dynamics.