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.