How does catalyst affect reaction rate

The oxidation of sulfur dioxide with dioxygen into sulfur trioxide in the presence of nitrogen oxides as the catalyst. In the given reaction, both the reactant and catalyst are in the same phase i. If the reactant and the catalysts are in different phases, they are said to be heterogeneous catalysis. Sulfur dioxide oxidized to sulfur trioxide in the presence of Pt. Here the catalyst is in a solid phase while the reactant in the gaseous phase.

In the presence of nickel as a catalyst, hydrogenation of vegetable oils. Here one reactant is in the liquid phase while the catalyst is in a solid phase. The reactant molecules must have threshold energy for reactants to react and give a product, and the number of molecules with this energy should also be above the threshold value. Activation Energy is the name of this basic energy. Only those reactant molecules would be able to form products that have energy above the energy of activation.

Catalyst adjusts this activation energy or has a different mechanism of reaction that needs lower activation energy to form products. In intermediate-complex theory, the role of a catalyst in chemical reactions is best explained. To increase the rate of a reaction, the number of successful collisions must be increased. One possible way of doing this is to provide an alternative way for the reaction to happen which has a lower activation energy.

In other words, to move the activation energy to the left on the graph:. Adding a catalyst has this effect on activation energy. A catalyst provides an alternative route for the reaction with a lower activation energy. This is illustrated on the following energy profile:. Care must be taken when discussing how a catalyst operates.

It does not "lower the activation energy of the reaction". There is a subtle difference between the two statements that is easily illustrated with a simple analogy.

Suppose there is a mountain between two valleys such that the only way for people to get from one valley to the other is over the mountain.

Skip to main content. Chemical Kinetics. Search for:. Factors that Affect Reaction Rate. Learning Objective Explain how concentration, surface area, pressure, temperature, and the addition of catalysts affect reaction rate.

Key Points When the concentrations of the reactants are raised, the reaction proceeds more quickly. This is due to an increase in the number of molecules that have the minimum required energy. For gases, increasing pressure has the same effect as increasing concentration. When solids and liquids react, increasing the surface area of the solid will increase the reaction rate.

This is due to an increase in the number of particles that have the minimum energy required. The reaction rate decreases with a decrease in temperature. Catalysts can lower the activation energy and increase the reaction rate without being consumed in the reaction. Differences in the inherent structures of reactants can lead to differences in reaction rates.

Molecules joined by stronger bonds will have lower reaction rates than will molecules joined by weaker bonds, due to the increased amount of energy required to break the stronger bonds.

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