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Reversible reactions and equilibria

Reversible reactions and equilibria

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Question 12

The flow diagram shows how formaldehyde is manufactured from methane in an industrial process:

Methane, Oxygen, Water→Carbon monoxide→Methanol→Formaldehyde→Formic acid \text{Methane, Oxygen, Water} \rightarrow \text{Carbon monoxide} \rightarrow \text{Methanol} \rightarrow \text{Formaldehyde} \rightarrow \text{Formic acid} Methane, Oxygen, Water→Carbon monoxide→Methanol→Formaldehyde→Formic acid

The carbon monoxide needed can be formed by the partial oxidation of methane gas.

a.

Balance the equation for this reaction:

…CH4+…O2→…CO+…H2O \dots\text{CH}_4 + \dots\text{O}_2 \rightarrow \dots\text{CO} + \dots\text{H}_2\text{O} …CH4​+…O2​→…CO+…H2​O
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b.

The equation for the catalytic synthesis of methanol from carbon monoxide and hydrogen (Reaction 2) is:

CO(g)+2H2(g)⇌CH3OH(g)ΔH=−91 kJ/mol \text{CO}\text{(g)} + 2\text{H}_2\text{(g)} \rightleftharpoons \text{CH}_3\text{OH}\text{(g)} \quad \Delta H = -91\text{ kJ/mol} CO(g)+2H2​(g)⇌CH3​OH(g)ΔH=−91 kJ/mol

Assuming that this reaction reaches equilibrium, explain what happens to the yield of methanol if the reaction is carried out at a higher pressure but at the same temperature.

[2]
c.

Assuming that this reaction reaches equilibrium, explain what happens to the yield of methanol if the reaction is carried out at a higher temperature but at the same pressure.

[2]
d.

Reaction 2 can be represented on an energy profile. Explain how the energy level of the products compares to the reactants and how the enthalpy change (ΔH\Delta HΔH) is shown on an energy profile diagram for this reaction.

[2]
e.

Reaction 2 is carried out using a copper-zinc catalyst. State the effect, if any, of using a catalyst on the enthalpy change for the reaction.

[1]
f.

Explain how a catalyst increases the rate of a reaction.

[2]
g.

The equations for some of the other reactions used in this manufacturing process are:

  • Reaction 3: CH4+H2O→CO+3H2\text{CH}_4 + \text{H}_2\text{O} \rightarrow \text{CO} + 3\text{H}_2CH4​+H2​O→CO+3H2​
  • Reaction 4: CO+2H2⇌CH3OH\text{CO} + 2\text{H}_2 \rightleftharpoons \text{CH}_3\text{OH}CO+2H2​⇌CH3​OH
  • Reaction 5: CH3OH+HCl→CH3Cl+H2O\text{CH}_3\text{OH} + \text{HCl} \rightarrow \text{CH}_3\text{Cl} + \text{H}_2\text{O}CH3​OH+HCl→CH3​Cl+H2​O
  • Reaction 6: CH3Cl+NH3→CH3NH2+HCl\text{CH}_3\text{Cl} + \text{NH}_3 \rightarrow \text{CH}_3\text{NH}_2 + \text{HCl}CH3​Cl+NH3​→CH3​NH2​+HCl

Explain which two of these are redox reactions.

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h.

A manufacturer produces a batch of 240 kg240\text{ kg}240 kg of methanol (CH3OH\text{CH}_3\text{OH}CH3​OH). Calculate the maximum mass of formaldehyde (HCHO\text{HCHO}HCHO) that can be made from this mass of methanol, using the overall reaction:

CH3OH+12O2→HCHO+H2O \text{CH}_3\text{OH} + \frac{1}{2}\text{O}_2 \rightarrow \text{HCHO} + \text{H}_2\text{O} CH3​OH+21​O2​→HCHO+H2​O

(Relative atomic masses: H=1\text{H} = 1H=1, C=12\text{C} = 12C=12, O=16\text{O} = 16O=16). Give a unit for your answer.

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Markscheme

Reversible reactions and equilibria Questions

  1. IGCSE
  2. /Chemistry
  3. /Reversible reactions and equilibria

28 exam-style questions on Edexcel IGCSE Chemistry Reversible reactions and equilibria. Each one has a worked solution and a mark scheme showing where the marks go.

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