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Chemical equilibria, Le Chatelier’s principle and Kc​

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Question 9

Compounds A and B react together to form an equilibrium mixture containing compounds C and D according to the equation:

A(aq)+2B(aq)⇌3C(aq)+D(aq) \text{A}(\text{aq}) + 2\text{B}(\text{aq}) \rightleftharpoons 3\text{C}(\text{aq}) + \text{D}(\text{aq}) A(aq)+2B(aq)⇌3C(aq)+D(aq)
1.

A beaker contained 50 cm3 of a 0.20 mol dm-3 aqueous solution of A. 1.5 × 10-2 mol of B and 2.0 × 10-2 mol of C were added to the beaker and the mixture was left to reach equilibrium. The equilibrium mixture formed contained 6.0 × 10-3 mol of A.

Calculate the amounts, in moles, of B, C and D in the equilibrium mixture.

[4]
2.

Give the expression for the equilibrium constant (KcK_cKc​) for this equilibrium and its units.

[2]
3.

A different equilibrium mixture of these four compounds, at a different temperature, contained 0.18 mol of B, 0.84 mol of C and 0.054 mol of D in a total volume of 4.00 × 102 cm3 of solution. At this temperature the numerical value of Kc K_c\,Kc​ was 82.

Calculate the concentration of A, in mol dm−3\text{mol dm}^{-3}mol dm−3, in this equilibrium mixture. Give your answer to the appropriate number of significant figures.

[4]
4.

Justify the statement that adding more water to the equilibrium mixture in Part 3 will lower the amount of A in the mixture.

[3]
Markscheme

Chemical equilibria, Le Chatelier’s principle and Kc Questions

  1. A Level
  2. /Chemistry
  3. /Chemical equilibria, Le Chatelier’s principle and Kc

24 exam-style questions on AQA A Level Chemistry Chemical equilibria, Le Chatelier’s principle and $K_c$, covering Chemical equilibria and Le Chatelier's principle and Equilibrium constant $K_c$ for homogeneous systems. Each one has a worked solution and a mark scheme showing where the marks go.

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