topic 9 Reversible Reactions and Equilibrium (1)

Topic 9 - Reversible Reactions and Equilibrium

Introduction

• Prepared by Mrs. Haneen Kheir

• Pages: 185 - 202

Page 2: Irreversible Reactions

• Most chemical reactions are irreversible.

  • Products cannot readily revert to reactants.

  • Examples:

    • Wood burning cannot revert to unburnt wood.

    • Reaction of magnesium with hydrochloric acid leads to magnesium chloride and hydrogen, which are difficult to convert back to magnesium.

Page 4: What are Reversible Reactions?

• Reversible reactions can easily convert back to reactants under certain conditions.

  • Generally represented as:

    • A + B ⇌ C + D

  • Products C and D can revert to reactants A and B.

Page 5: Dehydration of Hydrated Copper Sulfate

• Hydrated Copper (II) Sulfate crystals (blue) lose water upon heating.

  • Change: Blue crystals → White powder + Colourless liquid

  • Outcome:

    • Anhydrous Copper (II) Sulfate (white powder)

    • Water (colourless liquid)

Page 7: Heating Ammonium Chloride

• Heating ammonium chloride results in white crystals disappearing and reappearing higher up, with colourless gas formation.

  • Decomposes into: Ammonia (NH3) and Hydrogen Chloride (HCl)

Page 9: Equilibrium

• A reversible chemical reaction is a dynamic process; reactions occur in both forward and backward directions.

• In a closed container:

  • No substances are added or removed.

  • Reactions maintain dynamic equilibrium, which does not reach a static end.

Page 12: Characteristics of Equilibrium

• Equilibrium has several properties:

  • Both reactants and products are present continuously.

  • The system is dynamic, moving in both directions.

  • Concentrations of products and reactants remain constant.

  • Forward reaction rate equals reverse reaction rate.

  • Position of equilibrium can be changed by altering conditions.

Page 19: Predicting Changes to Equilibrium

• When applying changes, the system opposes that change.

• Influencing factors:

  1. Temperature

  2. Pressure

Page 20: Effect of Pressure

• Pressure influences the equilibrium position in reactions involving gases.

  • Increasing pressure shifts equilibrium to the side with fewer gaseous molecules.

Page 25: Effect of Temperature

• The enthalpy change (ΔH) for the forward reaction is indicated:

  • Negative ΔH = Exothermic reaction.

  • Reverse reaction is endothermic.

• Temperature changes affect reactants/products; decreasing favors exothermic reactions (shift right).

Page 29: Effect of Catalysts

• Catalysts speed up both forward and reverse reactions equally.

• They do not impact the position of equilibrium but do ensure that equilibrium is reached faster.

Page 51: Haber Process

• Produces ammonia from nitrogen and hydrogen in a reversible reaction.

  • Reaction: N2 + 3H2 ⇌ 2NH3

• Ammonia is vital for fertilizers, but achieving high yield is a challenge.

Page 58: Summary - Haber Process

• Conditions for optimum yield:

  • Pressure: 200 atm

  • Temperature: 380-450°C

  • Catalyst: Iron

• Yield factors:

  • Low temperature favors greater yield;

  • High pressure reduces gaseous volume and raises yield potential.

Page 62: Contact Process

• Sulfuric acid production through the contact process is also a reversible reaction reaching equilibrium.

  • Conditions: 400-450 °C, 2 atmospheres, with V2O5 catalyst.

Dynamic Equilibrium Summary

• Dynamic equilibrium reacts to changes, shifting to oppose effects of temperature, pressure, or concentrations.