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

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Question 19
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This question is about some gas mixtures at equilibrium.

This reaction can be used to produce nitrogen monoxide:

N2(g)+O2(g)⇌2NO(g)ΔH=+180.6 kJ mol−1\text{N}_2(\text{g}) + \text{O}_2(\text{g}) \rightleftharpoons 2\text{NO}(\text{g}) \quad \Delta H = +180.6\text{ kJ mol}^{-1}N2​(g)+O2​(g)⇌2NO(g)ΔH=+180.6 kJ mol−1

A mixture of 4.00 mol4.00\text{ mol}4.00 mol of N2(g)\text{N}_2(\text{g})N2​(g) and 4.00 mol4.00\text{ mol}4.00 mol of O2(g)\text{O}_2(\text{g})O2​(g) is allowed to reach equilibrium at a constant temperature in a 15.0 dm315.0\text{ dm}^315.0 dm3 container.

At equilibrium, there are 2.40 mol2.40\text{ mol}2.40 mol of NO(g)\text{NO}(\text{g})NO(g).

a.

Calculate the mole fraction of NO(g)\text{NO}(\text{g})NO(g) in the equilibrium mixture.

[3]
b.

State why the equilibrium constant (KpK_{\text{p}}Kp​) for this reaction has no units.

[1]
c.

The temperature of the equilibrium mixture is increased. How does the amount of NO(g)\text{NO}(\text{g})NO(g) change when the new position of equilibrium is reached? Select one:

  • The amount decreases.
  • The amount does not change.
  • The amount increases.
[1]
d.

Ethanol can be synthesized industrially by the direct hydration of ethene:

C2H4(g)+H2O(g)⇌C2H5OH(g)ΔH=−46 kJ mol−1\text{C}_2\text{H}_4(\text{g}) + \text{H}_2\text{O}(\text{g}) \rightleftharpoons \text{C}_2\text{H}_5\text{OH}(\text{g}) \quad \Delta H = -46\text{ kJ mol}^{-1}C2​H4​(g)+H2​O(g)⇌C2​H5​OH(g)ΔH=−46 kJ mol−1

The table below shows the mole fractions of each gas in an equilibrium mixture at a total pressure of 5000 kPa5000\text{ kPa}5000 kPa.

GasMole fraction
Ethene, C2H4\text{C}_2\text{H}_4C2​H4​0.4200.4200.420
Steam, H2O\text{H}_2\text{O}H2​O0.4800.4800.480
Ethanol, C2H5\text{C}_2\text{H}_5C2​H5​OH0.1000.1000.100

Give an expression for KpK_{\text{p}}Kp​ for this reaction.

[1]
e.

Calculate the value of KpK_{\text{p}}Kp​ at 5000 kPa5000\text{ kPa}5000 kPa. State the units.

[3]
f.

State the effect, if any, of an increase in the volume of the container on the value of KpK_{\text{p}}Kp​ for this reaction at a constant temperature.

[1]

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)