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

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Question 22
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Nitrosyl chloride decomposes on heating to form an equilibrium mixture containing nitrogen monoxide and chlorine gas:

2NOCl(g)⇌2NO(g)+Cl2(g)2\text{NOCl}(\text{g}) \rightleftharpoons 2\text{NO}(\text{g}) + \text{Cl}_2(\text{g})2NOCl(g)⇌2NO(g)+Cl2​(g)

a.

A sample of nitrosyl chloride was heated and allowed to reach equilibrium at a given temperature. The equilibrium mixture contained 7.20 g7.20\text{ g}7.20 g of nitrogen monoxide. Calculate the mass, in ggg, of chlorine gas in the equilibrium mixture.

[3]
b.

A different mass of nitrosyl chloride was heated and allowed to reach equilibrium at 650 K650\text{ K}650 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
nitrosyl chloride0.600
nitrogen monoxide1.80
chlorine0.600

For this reaction at 650 K650\text{ K}650 K, the equilibrium constant, Kp=3.60×105 PaK_p = 3.60 \times 10^5\text{ Pa}Kp​=3.60×105 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 650 K650\text{ K}650 K (3.60×105 Pa3.60 \times 10^5\text{ Pa}3.60×105 Pa) to calculate the value of KpK_pKp​ at 650 K650\text{ K}650 K for the following equilibrium:

NOCl(g)⇌NO(g)+12Cl2(g)\text{NOCl}(\text{g}) \rightleftharpoons \text{NO}(\text{g}) + \frac{1}{2}\text{Cl}_2(\text{g})NOCl(g)⇌NO(g)+21​Cl2​(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)