5. Catalysis. Homogeneous and heterogeneous catalysis. Autocatalysis. Chemical equilibrium - basic conceptions, principle of Le Chatelier's. Factors influencing on the chemical equilibrium.

Catalysts

• Definition:
• A substance that increases the rate of a chemical reaction.
• Remains unchanged qualitatively and quantitatively after the reaction.
• Does not affect the overall change in Gibbs energy (ΔG) of the reaction.
• Function:
• Lowers the activation energy of the reaction, making it easier for molecules to react.
• Acts like a matchmaker for reacting molecules, accelerating the reaction.

• Characteristics:
• Not consumed in the reaction.
• Can be biological (enzymes) or synthetic materials.
• Plays a crucial role in many industrial processes and biological functions.
• Examples:
• Platinum catalyst in car catalytic converters.
• Enzyme lactase for digesting lactose.

Mechanism of Catalyst Operation:

• Catalysts vs. Promoters vs. Inhibitors:
• Catalysts: Lower the activation energy of a reaction, increasing the rate without being consumed.
• Promoters: Similar to catalysts, they accelerate reactions but are consumed during the process.
• Inhibitors: Decrease the reaction rate by increasing the activation energy or hindering interactions between reactants.
• Mechanism of Catalysis:
• Catalysts provide an alternative reaction pathway with a lower activation energy compared to the uncatalyzed reaction.
• This alternative pathway involves intermediate steps that are more energetically favourable, allowing the overall reaction to proceed faster.

• The catalyst itself undergoes temporary changes during these intermediate steps but ultimately returns to its original form by the end of the reaction cycle.
• Types of Catalysis:
• Homogeneous: Catalyst and reactants are in the same phase (e.g., liquid or gas).
• Heterogeneous: Catalyst and reactants are in different phases (e.g., solid catalyst and liquid reactants). The reaction occurs at the interface between phases.

• Autocatalysis: In autocatalysis, the reaction is catalysed by one of its products. One of the simplest examples of this is in the oxidation of a solution of ethanedioic acid (oxalic acid) by an acidified solution of potassium manganate(VII) (potassium permanganate).
• Intramolecular: A functional group within the reactant molecule itself facilitates the reaction by bringing reacting atoms closer or stabilizing intermediates.