Consider the reaction: H2(g) + I2(g) ⇌ 2 HI(g). A reaction mixture in a 3.67-L flask at a certain temperature initially contains 0.763 g H2 and 96.9 g I2. At equilibrium, the flask contains 90.4 g HI. Calculate the equilibrium constant (Kc) for the reaction at this temperature.

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Convert the initial masses of H2 and I2 to moles using their molar masses: \( \text{moles of } H_2 = \frac{0.763 \text{ g}}{2.02 \text{ g/mol}} \) and \( \text{moles of } I_2 = \frac{96.9 \text{ g}}{253.8 \text{ g/mol}} \).

Convert the mass of HI at equilibrium to moles using its molar mass: \( \text{moles of } HI = \frac{90.4 \text{ g}}{127.9 \text{ g/mol}} \).

Determine the change in moles of HI from the initial state to equilibrium, and use stoichiometry to find the changes in moles of H2 and I2.

Calculate the equilibrium moles of H2 and I2 by subtracting the change in moles from their initial moles.

Use the equilibrium concentrations (moles/volume) of H2, I2, and HI to calculate the equilibrium constant \( K_c = \frac{[HI]^2}{[H_2][I_2]} \).

Key Concepts

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

Equilibrium Constant (Kc)

The equilibrium constant (Kc) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a reversible chemical reaction. It is calculated using the formula Kc = [products]^[coefficients] / [reactants]^[coefficients], where the concentrations are in molarity. A larger Kc indicates a greater concentration of products at equilibrium, while a smaller Kc suggests that reactants are favored.

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It allows us to determine the moles of substances involved in the reaction, which is essential for calculating concentrations. In this case, converting the masses of H2 and I2 to moles is necessary to find their concentrations in the equilibrium expression.

Equilibrium Position

The equilibrium position refers to the state of a reversible reaction where the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. Understanding the initial concentrations and the changes that occur as the reaction reaches equilibrium is crucial for calculating Kc. In this scenario, knowing the amount of HI at equilibrium helps in determining how much H2 and I2 remain.

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