Home >> Science & Nature >> Science

What Effect Does the Addition of a Catalyst Have on a Chemical Reaction at Equilibrium?

Catalysts make life possible. Without the protein catalysts called enzymes, the reactions that your cells need to function would be too slow or would not occur. Catalysts are also important for chemists working to synthesize new products or make existing syntheses more efficient. When thinking about how these catalysts work, it's crucial to realize that the catalyst does not change the equilibrium of a chemical reaction -- it just helps the system get there more rapidly.

Catalysts &Life
- Combining sucrose (table sugar) and oxygen to make carbon dioxide and water is a spontaneous reaction. If you just mixed sugar and air in a jar at room temperature, however, no reaction would occur. Many of the reactions essential to life are similar in that they are extremely slow under the conditions found in cells. That's why catalysts are absolutely essential; by speeding up these reactions, they enable cells to produce the molecules they need to function.
Equilibrium
- Chemical equilibrium is the point when a reaction is still occurring, but the concentration of reactants and products is no longer changing, because the reverse and forward reactions are happening at equal rates. The product-reactant ratio at equilibrium is dictated by the thermodynamics of the reaction -- the relative stability of products and reactants. A catalyst has no effect on equilibrium concentrations. Consequently, if you added a catalyst to a system already at equilibrium, there would be no change.
Reaction Rate
- Catalysts don't change the equilibrium, they just hurry things up so that you get to the equilibrium more rapidly. Take sucrose, for example. Under ordinary conditions in your cells, sucrose doesn't break down fast enough to supply the energy your cells need. By using enzymes, your cells accelerate the breakdown of sucrose so it happens much more quickly. At the same time, the enzymes ensure this process happens in a controlled way through a sequence of small steps that can be regulated efficiently.
Mechanism
- Ultimately, the role of a catalyst is to provide a different mechanism for the reaction -- a mechanism that's faster than the one that would otherwise take place. Acids and bases are important catalysts in many industrial processes (sulfuric acid, for example, is a useful catalyst in many reactions). Transition metals such as iron and platinum are also important catalysts; the catalytic converter in your car, for example, uses a platinum catalyst to accelerate the conversion of carbon monoxide and unburned hydrocarbons to CO2, thereby reducing the amount of these pollutants in the exhaust.

Science