Equilibrium constant $K_p$ for homogeneous systems (A-level only)

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Question 25
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Sulfur trioxide decomposes at high temperatures to form an equilibrium mixture containing sulfur dioxide and oxygen:

2SO3(g)⇌2SO2(g)+O2(g)2\text{SO}_3(\text{g}) \rightleftharpoons 2\text{SO}_2(\text{g}) + \text{O}_2(\text{g})2SO3​(g)⇌2SO2​(g)+O2​(g)

a.

A sample of sulfur trioxide was heated and allowed to reach equilibrium at a given temperature. The equilibrium mixture contained 12.82 g12.82\text{ g}12.82 g of sulfur dioxide. Calculate the mass, in ggg, of oxygen gas in the equilibrium mixture (take relative atomic masses: S=32.1S = 32.1S=32.1, O=16.0O = 16.0O=16.0).

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b.

A different mass of sulfur trioxide was heated and allowed to reach equilibrium at 1000 K1000\text{ K}1000 K.

Table 1: Amounts of substances at equilibrium \text{Table 1: Amounts of substances at equilibrium} Table 1: Amounts of substances at equilibrium
SubstanceAmount at equilibrium / mol
sulfur trioxide0.600
sulfur dioxide1.80
oxygen0.600

For this reaction at 1000 K1000\text{ K}1000 K, the equilibrium constant, Kp=2.70×105 PaK_p = 2.70 \times 10^5\text{ Pa}Kp​=2.70×105 Pa.

  • (i) Calculate the mole fraction of each substance at equilibrium.
  • (ii) Give the expression for the equilibrium constant, KpK_pKp​.
  • (iii) Calculate the total pressure, in PaPaPa, of this equilibrium mixture.
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c.

Use the value of KpK_pKp​ at 1000 K1000\text{ K}1000 K (2.70×105 Pa2.70 \times 10^5\text{ Pa}2.70×105 Pa) to calculate the value of KpK_pKp​ at 1000 K1000\text{ K}1000 K for the following equilibrium:

SO3(g)⇌SO2(g)+12O2(g)\text{SO}_3(\text{g}) \rightleftharpoons \text{SO}_2(\text{g}) + \frac{1}{2}\text{O}_2(\text{g})SO3​(g)⇌SO2​(g)+21​O2​(g)

Deduce the units of this new KpK_pKp​.

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Equilibrium constant $K_p$ for homogeneous systems (A-level only) Questions

  1. A Level
  2. /Chemistry
  3. /Equilibrium constant $K_p$ for homogeneous systems (A-level only)