Factors that change the speed of chemical reactions (continued)


Catalyst It is a chemical that does not participate in the chemical reaction. Decreases activation energy and increases reaction speed.

The catalyst accelerates the reaction but does not change the chemical composition of the reagents and products involved. The amount of substance produced in the reaction does not change with the use of catalysts.

If the reaction is reversible, the reverse reaction will also be accelerated because its activation energy will also have a lower value. The catalyst does not change the enthalpy variation.

Graphics with and without catalysts:


Catalysis is the increase in reaction speed caused by the catalyst. The word catalysisfrom greek katálysis, was introduced in 1835 by Berzeliu.

In our body there are many catalysts, which are called enzymes. Saliva and gastric juice (which contain hydrochloric acid) are examples of enzymes that increase the speed of reaction, in this case digestion.

In chemical industries, especially petrochemicals, catalysts are widely used to accelerate reactions, making the process cheaper.

One way to see the action of catalysts is by adding sugar to the soda. Carbonated refrigerenates contain carbon dioxide (carbon dioxide) and can be eliminated more easily with added sugar. The gas elimination reaction takes place more rapidly and the gas bubbles form leaving the solution.

In the chemical equation, the catalyst is placed over the arrow representing the chemical reaction. Depending on the physical states of the reagents and products, catalysis may be homogeneous or heterogeneous.

- homogeneous catalysis: when reagents and catalyst are in the same physical state, forming a single phase system.

- heterogeneous catalysis: when reagents and catalyst are not in the same physical state, forming a heterogeneous system.

There is no ideal type of catalyst. For each chemical reaction there is a different type of catalyst. The most common catalysts are:

- metals - mainly transition metals: Co, Ni, Pt, Pd
- acids - which catalyze many organic reactions: H2SO4
- metal oxides - Al2O3, Fe2O3
- bases - NaOH
- enzymes - produced by living organisms: lipase, gastric juice.


They are substances that, unlike catalysts, increase the activation energy and, as a consequence, slow down the chemical reaction.

The inhibitor may also be called a catalyst poison or anticatalyst. It was formerly called the negative catalyst.

Instantaneous velocity

In chemical reactions, the velocity at each instant is different from the average velocity. The instantaneous velocities are never the same, having different values ​​during the reaction.

If the time intervals used to measure the average velocity get smaller and smaller, the average velocity will tend to assume values ​​closer to the velocity at a certain moment.

Instantaneous velocity It is the value to which the average velocity tends when the time intervals get smaller and smaller.

Can be calculated according to “Kinetic Law or Speed ​​equation”Proposed by Guldberg and Waage.