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

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Question 16
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Nitrosyl chloride decomposes at an elevated temperature according to the following equation:

2NOCl(g)⇌2NO(g)+Cl2(g)ΔH=+76 kJ mol−12\text{NOCl}(\text{g}) \rightleftharpoons 2\text{NO}(\text{g}) + \text{Cl}_2(\text{g}) \quad \Delta H = +76\text{ kJ mol}^{-1}2NOCl(g)⇌2NO(g)+Cl2​(g)ΔH=+76 kJ mol−1

1.

A 0.800 mol0.800\text{ mol}0.800 mol sample of nitrosyl chloride is sealed in a container and heated at a constant temperature until equilibrium is established. At equilibrium, the system is found to contain 0.240 mol0.240\text{ mol}0.240 mol of chlorine gas. Calculate the mole fraction of each substance at equilibrium. Give your answers to 3 decimal places.

  • Mole fraction of NOCl\text{NOCl}NOCl
  • Mole fraction of NO\text{NO}NO
  • Mole fraction of Cl2\text{Cl}_2Cl2​
[3]
2.

The total pressure in the container in Part 1 is 220 kPa220\text{ kPa}220 kPa at equilibrium. Calculate the partial pressure, in kPa\text{kPa}kPa, of NOCl\text{NOCl}NOCl. (If you were unable to answer Part 1, assume that the mole fraction of NOCl\text{NOCl}NOCl is 0.3500.3500.350. This is not the correct answer.)

[1]
3.

The table below shows the mole fractions of the three components in a different equilibrium mixture of the same system:

GasMole fraction
NOCl\text{NOCl}NOCl0.4000.4000.400
NO\text{NO}NO0.4000.4000.400
Cl2\text{Cl}_2Cl2​0.2000.2000.200

For this specific equilibrium mixture, Kp=44.0 kPaK_p = 44.0\text{ kPa}Kp​=44.0 kPa.

  • Give the expression for KpK_pKp​ for this reaction.
  • Use your expression and the data in the table to calculate the total pressure, in kPa\text{kPa}kPa, in the container.
[3]
4.

The equilibrium mixture in Part 3 is compressed into a smaller volume at constant temperature. Deduce the effect, if any, of this volume reduction on the equilibrium yield of chlorine and on the numerical value of KpK_pKp​.

  • Effect on yield of chlorine
  • Effect on KpK_pKp​
[2]
5.

The equilibrium mixture in Part 3 is allowed to reach a new equilibrium at a lower temperature. Explain why the equilibrium yield of chlorine decreases.

[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)