- Catalyst: chemical agent that speeds up a reaction without being consumed by the reaction → can be used over and over again
○ Do not affect the free energy/enthalpy of a reaction!
○ Reactions with a catalyst will typically require at least 2 steps
- Catalysts allow reactions to occur with a lower AE → more reactant molecules will have the new, minimum Ea to collide and form products → reaction rate increased
- Homogeneous catalyst: is present in the same phase as the reacting molecules
- Heterogeneous catalyst: exists in a different phase (usually as a solid; a catalytic converter is one type)
○ 4 steps of heterogeneous catalysis
- Adsorption (collection of one substance on the surface of another substance) and activation of the reactants
- Migration of the adsorbed reactants on the surface
- Reaction of the adsorbed substances
- Escape (desorption) of the products
How Catalysts Speed Up Reactions
- A catalyst increases the rate constant and lowers Ea Barrier by…
○ Forming a more stable activated complex
○ Increased collision frequency
○ Improved orientation effects
- Allow chemical reactions to occur at lower temperatures
- Speeds up natural reactions ≠ cause them
- Reactions can occur without catalysts, but would be slower & cost a lot more energy
Activation Energy Barrier
- Activation Energy: total amount of energy needed for reactants to become products
- Reacting molecules must collide and have enough energy (AE) needed to reach transition state and break bonds of reactants
○ Activation energy often heat from environment
■ But bad bcuz speeds up all reactions, denatures proteins & kills cells
- Transition State: reactive (unstable) condition of the substrate after enough energy has been absorbed to start the reaction
