MA

topic 9 Reversible Reactions and Equilibrium (1)

Topic 9 - Reversible Reactions and Equilibrium

Irreversible Reactions

  • Most chemical reactions are irreversible; the products cannot easily revert to reactants.

    • Example: Wood burning cannot be changed back to unburnt wood.

    • Reaction of magnesium with hydrochloric acid produces magnesium chloride and hydrogen, which cannot be easily reversed.

Reversible Reactions

  • Reversible reactions occur when the reverse reaction is easy under certain conditions.

  • General Equation for reversible reactions:

    • A + B ⇌ C + D

      • Reactants A and B convert into products C and D, which can also revert back to A and B.

Dehydration of Hydrated Copper Sulfate

  • Hydrated Copper (II) Sulfate crystals are blue in color.

  • When heated, they lose water and turn into white Anhydrous Copper (II) Sulfate (white powder) and a colorless liquid (water).

  • Chemical change:

    • Heat Hydrated Copper (II) Sulfate ➔ Anhydrous Copper (II) Sulfate + Water

Heating Ammonium Chloride

  • Heating ammonium chloride causes white crystals to disappear and reappear further up the test tube, resulting in the formation of colorless gas (ammonia) and hydrogen chloride gas.

  • Reaction:

    • NH4Cl (s) ⇌ NH3 (g) + HCl (g)

  • The gases recombine in cooler areas, forming a white solid (NH4Cl).

Equilibrium

  • Reversible reactions are dynamic; both forward and reverse reactions occur simultaneously and constantly, particularly in a sealed container where no substances escape or enter.

  • At equilibrium, the concentrations of reactants and products remain constant, and the rates of forward and reverse reactions are equal.

Characteristics of Equilibrium

  • Both reactants and products are present continuously.

  • Equilibrium can be approached from either direction.

  • Dynamic - constantly shifts to oppose changes in conditions.

Effect of Pressure on Equilibrium

  • Changes in pressure affect the position of equilibrium in reactions involving gases:

    • Increase in pressure favors reactions that produce fewer moles of gas.

    • Example: N2 + 3H2 ⇌ 2NH3 (pressure increase shifts equilibrium to the right).

  • If the number of gaseous molecules is equal on both sides, pressure will have no effect on equilibrium.

Effect of Temperature on Equilibrium

  • Changing temperature affects equilibrium:

    • Decreasing temperature favors exothermic reactions.

    • Increasing temperature favors endothermic reactions.

Effect of Concentration on Equilibrium

  • Changes in concentration will shift equilibrium to oppose the change:

    • Increase in concentration of a reactant shifts equilibrium to the right.

    • Decrease in concentration shifts equilibrium to the left.

Haber Process

  • Industrial process for producing ammonia via the reaction of nitrogen with hydrogen:

    • N2(g) + 3H2(g) ⇌ 2NH3(g)

  • Conditions for optimal production:

    • Pressure: 200 atm

    • Temperature: 380-450 °C

    • Catalyst: iron

Factors Impacting Yield and Production in Haber Process

  • Low temperature increases yield due to exothermic nature.

  • High pressure increases collisions and reaction rates.

  • Compromise conditions are used to balance yield, rate of reaction, and production costs.

Contact Process

  • Involves the production of sulfuric acid through a reversible reaction.

  • Optimal conditions:

    • Temperature: 400-450 °C

    • Pressure: 2 atm

    • Catalyst: vanadium (V) oxide (V2O5)

Overall Summary

  • Reversible reactions are crucial for industrial processes due to their dynamic nature, allowing for yield optimization through the careful manipulation of temperature, pressure, and concentration.

  • Understanding equilibrium is essential for harnessing chemical reactions in practical applications.