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Ch.15 - Chemical Equilibrium
All textbooksMcMurry 8th EditionCh.15 - Chemical EquilibriumProblem 86
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Chapter 15, Problem 86

A sample of HI 19.30 * 10^-3 mol^2 was placed in an empty 2.00-L container at 1000 K. After equilibrium was reached, the concentration of I2 was 6.29 * 10^-4 M. Calculate the value of Kc at 1000 K for the reaction H2(g) + I2(g) ⇌ 2 HI(g).

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1
Identify the balanced chemical equation for the reaction: \( \text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2 \text{HI}(g) \).
Write the expression for the equilibrium constant \( K_c \) for the reaction: \( K_c = \frac{[\text{HI}]^2}{[\text{H}_2][\text{I}_2]} \).
Determine the initial concentration of HI by dividing the initial moles by the volume of the container: \( \frac{19.30 \times 10^{-3} \text{ mol}}{2.00 \text{ L}} \).
Use the stoichiometry of the reaction to express the changes in concentration of \( \text{H}_2 \), \( \text{I}_2 \), and \( \text{HI} \) in terms of a variable \( x \), where \( x \) is the change in concentration of \( \text{I}_2 \) at equilibrium.
Substitute the equilibrium concentrations into the \( K_c \) expression and solve for \( K_c \).
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At 500 K, the equilibrium constant for the dissociation reaction H2(g) ⇌ 2H(g) is very small (Kc = 1.2 × 10⁻⁴²). (a) What is the molar concentration of H atoms at equilibrium if the equilibrium concentration of H2 is 0.10 M? (b) How many H atoms and H2 molecules are present in 1.0 L of 0.10 M H2 at 500 K?
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