The process of adsorption occurs on the surface of the iron metal, here the molecules are drawn very close together, where they react at lower activation energy, the product formed leaves and the same reaction site remains active for the same reaction to occur over and over again.
When the new reaction path has a lower activation energy, the rate of attainment of equilibrium is increased and the reaction is said to be catalysed. Substances that react with catalysts to reduce or eliminate their effect are called poisons.
N.B.
In the case of the Harber process, attainment of equilibrium is more rapid; but there is no increase in the yield of ammonia Heterogeneous and Homogeneous Catalysts Catalysts can be sub-divided again according to their phase in a reaction mixture: Heterogeneous catalysts - These catalysts are in a different phase to the reaction mixture.
For example solid magnesium dioxide catalysing the decomposition of hydrogen peroxide.
Homogeneous catalysts - theses catalysts are in the same phase as the reaction mixture For example dilute sulphuric acid catalysing an organic reaction, by acting as a proton donor.
Homogeneous catalysts verses Heterogeneous catalysts? Advantages/Disadvantages of homogeneous catalysts relative to heterogeneous catalysts Advantages Homogenous catalysts are generally: Far more selective for a single product Far more active Far more easily studied from chemical & mechanistic aspects Far more easily modified for optimizing electivity.
Disadvantages Far more sensitive to being poisoned (permanent deactivation via non-competitive inhibitors) Far more difficult for achieving product / catalyst separations. Because permanent deactivation is much more susceptible in homogeneous catalysts, it is a better choice for chemical industries to opt for heterogeneous catalysts, as they are much less prone to being poisoned. Another feature with heterogeneous catalysts is that the product leaving (especially gases) is free from the catalyst, as the product is in a different state to the catalyst.
With homogeneous catalysts it is recognised that there are costs and time involved when separating the homogeneous catalyst from the product. This is the reason why homogeneous catalysts are usually reserved for highly selective and complex reactions, especially in pharmaceutical manufacture. Familiar Uses of catalysts Some familiar uses of heterogeneous catalysts include: Platinum and other rare earth metals in catalytic converters Here the extremely finely divided metal surface (arranged as a honeycomb) acts as a reaction site for noxious gases that are emitted from the exhaust. For example the following reaction between carbon monoxide and nitrogen monoxide: 2CO + 2NO Platinum Catalyst 2CO2 + N2 is far too slow in uncatalysed conditions resulting in high emissions of the toxic carbon and nitrogen monoxides; this would also result in failing an M.O.T. test, when testing for emission percentages.
With the platinum blend catalyst, the reaction is rapid, with harmless carbon dioxide and nitrogen gas being the catalytic reaction products. Biological catalysts - Enzymes Enzymes belong to a specific group of proteins that are synthesised by living cells. They function as catalysts for the large number of biochemical reactions that constitute the metabolism of a cell and indeed a living organism. Mechanism of Enzyme Action Again enzymes function on the principle of catalysis, they reduce the activation energy of metabolic reactions in cells. There are a number of mechanisms by which this activation energy decrease may be achieved. The most important of these involves the enzyme initially binding the substrate(s) (specific reactant), in the correct orientation to react, close to the catalytic groups on the active enzyme complex and any other substrates.
This initial binding is known as the known as the formation of the enzyme-substrate complex. Whereby the enzyme forms a stabilising complex around the substrate and changes shape slightly to precisely fit the substrate molecule.
In this way the binding energy is used partially in order to reduce the contribution of the considerable activation entropy, towards the total activation energy, thus the reaction occurs more quickly at a lower temperature. The optimum activity of enzymes is usually is dependant on a certain pH ranges and temperatures of about 40-50oC Uses of Enzymes in Laundry detergents Many enzymes have been discovered, including fat, protein and carbohydrate digesting enzymes. Because of the temperatures they work best at (40-50oC) they have found use as additives to laundry detergents, known as biological detergents. The conclusions of this include: The washing machine can be set to a lower temperature to get rid of food and blood stains, so saving on electricity costs, and the damage caused to laundry by washing at high temperatures to get rid of stubborn fat, protein and carbohydrate associated stains.
Temperature, pH and enzyme activity Enzyme activity is usually closely dependant on pH and temperature. When an enzyme catalysed reaction proceeds increasing temperature will increase the rate of the reaction, up to a maximum - which is the optimum temperature of the enzyme, increasing the temperature beyond this results in no increase in the rate of the reaction. But has the opposite effect in that the enzyme is irreversibly damaged (denaturisation) because the high temperature disrupts the 3-D conformation of the enzyme, which is important in determining the formation of the enzyme-substrate complex.
With pH, there is no rise in activity if the pH is increased, but rather the pH the enzyme works best at is limited to a narrow range anywhere on the pH scale. Generally this pH lies usually at around neutral - slightly alkaline, but enzymes which are found in the stomach juices, have optimum pH ranges at around pH 2-3 which is not surprising considering the high acidity of the stomach juices contributed by the hydrochloric acid.
Summary Of Presentation In this presentation we have learned about the many applications of catalysis. Catalysts both biological and non-biological, work on the same principle. They reduce the activation energy (Eact) of a reaction, resulting in the attainment of equilibrium much faster.
Catalysts can be divided into two types Industrial (non-biological) catalysts - These include finely divided metals, specific compounds designated for certain reactions.
Biological catalysts (enzymes) are complex proteins, derived from living cells. These are employed in detergents, pharmaceuticals and pharmaceutical manufacture.
Enzymes can be irreversibly damaged by extremes of temperature and pH Catalysts can be categorised again; depending on the state they are when they are catalysing a reaction.
Heterogeneous catalysts are in a different phase to the reacting species, whilst homogeneous catalysts are in the same phase as the reacting species. Heterogeneous catalysts are generally the most used in industry as they are the most resistant to poisoning Homogeneous catalysts are reserved usually for complex reactions requiring catalysts with high selectivity for certain reagents i.e. in pharmaceutical drug manufacture.
Everyday applications for catalysts include use in catalytic converters and biological washing powders.
Catalysis is a valuable technology that has enabled us to get the most from chemical and petroleum resources. Costs, which are reduced by catalysis, are passed on to us, for example the anti - inflammatory drug cost 60 a gram in the 50's-60's. With the introduction of better synthesis routes and better catalysts, the cost of cortisone has been reduced to around 50 pence a gram.
