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

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Question 18
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Nitrogen dioxide decomposes on heating to form an equilibrium mixture containing nitrogen monoxide and oxygen:

2NO2(g)⇌2NO(g)+O2(g)2\text{NO}_2(\text{g}) \rightleftharpoons 2\text{NO}(\text{g}) + \text{O}_2(\text{g})2NO2​(g)⇌2NO(g)+O2​(g)

a.

A sample of nitrogen dioxide was heated and allowed to reach equilibrium at a given temperature. The equilibrium mixture contained 4.50 g4.50\text{ g}4.50 g of nitrogen monoxide. Calculate the mass, in g\text{g}g, of oxygen gas in the equilibrium mixture.

[2]
b.

A different mass of nitrogen dioxide was heated and allowed to reach equilibrium at 700 K700\text{ K}700 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
nitrogen dioxide0.400
nitrogen monoxide1.50
oxygen0.600

For this reaction at 700 K700\text{ K}700 K, the equilibrium constant, Kp=1.35×105 PaK_p = 1.35 \times 10^5\text{ Pa}Kp​=1.35×105 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 Pa\text{Pa}Pa, of this equilibrium mixture.
[5]
c.

Use the value of KpK_pKp​ at 700 K700\text{ K}700 K (1.35×105 Pa1.35 \times 10^5\text{ Pa}1.35×105 Pa) to calculate the value of KpK_pKp​ at 700 K700\text{ K}700 K for the following equilibrium:

NO2(g)⇌NO(g)+12O2(g)\text{NO}_2(\text{g}) \rightleftharpoons \text{NO}(\text{g}) + \frac{1}{2}\text{O}_2(\text{g})NO2​(g)⇌NO(g)+21​O2​(g)

Deduce the units of this new KpK_pKp​.

[2]

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)