Question:

Bromine monochloride, BrCl decomposes into bromine and chlorine and reaches the equilibrium:
\(2BrCl (g) ⇋ Br_2 (g) + Cl_2 (g)\)
for which Kc = 32 at 500 K. If initially pure BrCl is present at a concentration of 3.3 × 10–3 mol L–1, what is its molar concentration in the mixture at equilibrium?

Updated On: Nov 10, 2023
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Solution and Explanation

Let the amount of bromine and chlorine formed at equilibrium be x.
The given reaction is :
                                        \(2BrCl(g) ↔ Br_2(g) + Cl_2(g)\)

Initial conc.                      \(3.3×10^{-3}\)         \(0\)              0
At equilibrium             \(3.3×10^{-3}-2x\)    \(x\)              \(x\)

Now, we can write,
\(\frac {[Br_2][Cl_2]}{[BrCl]^2} = K_c\)

⇒ \(\frac {x×x}{(3.3×10^{-3}- 2x)^2} = 32\)

 ⇒ \(\frac {x}{(3.3×10^{-3}- 2x)} = 5.66\)
⇒ \(x = 18.678×10^{-3 }-11.32 x\)
⇒ \(12.32 x = 18.678×10^{-3}\)
⇒ \(x = 1.5×10^{- 3}\)
Therefore, at equilibrium,
\([BrCl] = 3.3×10^{-3}-(2×1.5×10^{-3})\)
\(3.3×10^{-3}-3.0×10^{-3}\)
\(0.3 × 10^{-3}\)
\(3.0×10^{- 4} \ mol L^{-1}\)

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Top Questions on Law Of Chemical Equilibrium And Equilibrium Constant

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Concepts Used:

Equilibrium Constant

The equilibrium constant may be defined as the ratio between the product of the molar concentrations of the products to that of the product of the molar concentrations of the reactants with each concentration term raised to a power equal to the stoichiometric coefficient in the balanced chemical reaction.

The equilibrium constant at a given temperature is the ratio of the rate constant of forwarding and backward reactions.

Equilibrium Constant Formula:

Kequ = kf/kb = [C]c [D]d/[A]a [B]b = Kc

where Kc, indicates the equilibrium constant measured in moles per litre.

For reactions involving gases: The equilibrium constant formula, in terms of partial pressure will be:

Kequ = kf/kb = [[pC]c [pD]d]/[[pA]a [pB]b] = Kp

Where Kp indicates the equilibrium constant formula in terms of partial pressures.

  • Larger Kc/Kp values indicate higher product formation and higher percentage conversion.
  • Lower Kc/Kp values indicate lower product formation and lower percentage conversion.

Medium Kc/Kp values indicate optimum product formation.

Units of Equilibrium Constant:

The equilibrium constant is the ratio of the concentrations raised to the stoichiometric coefficients. Therefore, the unit of the equilibrium constant = [Mole L-1]△n.

where, ∆n = sum of stoichiometric coefficients of products – a sum of stoichiometric coefficients of reactants.