Question:

1 mole of HI is heated in a closed container of capacity of 2 L. At equilibrium half a mole of HI is dissociated. The equilibrium constant of the reaction is 

Updated On: Sep 13, 2024
  • 0.25
  • 1
  • 0.35
  • 0.5
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The Correct Option is A

Solution and Explanation

To determine the equilibrium constant of the reaction, we need to know the balanced equation for the dissociation of HI. The balanced equation is: 2HI ⇌ H2 + I2 The expression for the equilibrium constant (Kc) is given by the equation: Kc = [H2] * [I2] / [HI]2 Given that at equilibrium half a mole of HI is dissociated, we can calculate the equilibrium concentrations: [HI] = 0.5 mole / 2 L = 0.25 M [H2] = 0.5 * 0.25 M = 0.125 M [I2] = 0.5 * 0.25 M = 0.125 M Substituting these values into the equilibrium constant expression, we have: Kc = (0.125 M) * (0.125 M) / (0.25 M)2 Kc = 0.015625 / 0.0625 Kc = 0.25 Therefore, the equilibrium constant of the reaction is (A) 0.25.

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Concepts Used:

Law of Chemical Equilibrium

Law of Chemical Equilibrium states that at a constant temperature, the rate of a chemical reaction is directly proportional to the product of the molar concentrations of the reactants each raised to a power equal to the corresponding stoichiometric coefficients as represented by the balanced chemical equation.

Let us consider a general reversible reaction;

A+B ↔ C+D

After some time, there is a reduction in reactants A and B and an accumulation of the products C and D. As a result, the rate of the forward reaction decreases and that of backward reaction increases. 

Eventually, the two reactions occur at the same rate and a state of equilibrium is attained. 

By applying the Law of Mass Action;

The rate of forward reaction;

Rf = Kf [A]a [B]b

The rate of backward reaction;

Rb = Kb [C]c [D]d

Where,

[A], [B], [C] and [D] are the concentrations of A, B, C and D at equilibrium respectively.

a, b, c, and d are the stoichiometric coefficients of A, B, C and D respectively.

Kf and Kb­ are the rate constants of forward and backward reactions.

However, at equilibrium,

Rate of forward reaction = Rate of backward reaction.

Kc is called the equilibrium constant expressed in terms of molar concentrations.

The above equation is known as the equation of Law of Chemical Equilibrium.