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Equilibrium concentrations from K and the initial amounts

This type of question, asked 3 times: 2021 Paper 16, 2021 Paper 19, 6 Apr 2026 S1. All 3 questions below, oldest first.

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  1. Question 1

    2021 Paper 16

    29
    PCl5⇌PCl3+Cl2, KC=1.844PCl_{5}\rightleftharpoons PCl_{3}+Cl_{2},{\text{ }K}_{C}= 1.844. If 3 moles of PCl5PCl_{5} are taken in 1 L1\text{ }L vessel. Find equilibrium concentration of PCl5PCl_{5}.

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  2. Question 2

    2021 Paper 19

    52
    The equilibrium constant KcK_{c} at 298 K298\text{ }K for the reaction A+B⇌C+DA + B \rightleftharpoons C + D is 100. Starting with an equimolar solution with concentrations of A,B,CA,B,C and DD all equal to 1M1M, the equilibrium concentration of DD is ____\_\_\_\_ ×10−2\times10^{- 2} M. (Nearest integer)

  3. Question 3

    6 Apr 2026 S1

    32
    One mole each of He and A(g)A(g) are taken in a 10 L closed flask and heated to 400 K to establish the following equilibrium.
    A(g)⇌B(g)A(g) \rightleftharpoons B(g)
    KCK_{C} for this reaction at 400 K is 4.0. The partial pressures (in atm ) of He and B(g)B(g) are respectively (at equilibrium). (Assume He,A(g)He,A(g) and B(g)B(g) behave as ideal gases) (Given : R=0.082 L atm K−1 mol−1R = 0.082\text{ }L\text{ }atm{\text{ }K}^{- 1}{\text{ }mol}^{- 1} )

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