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:
Temperature
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.