As you may have already noticed, some reactions occur faster and others more slowly. Therefore, reactions can be fast or slow and their speed can be measured by product formation or reagent consumption per unit time.
Suppose that in the reaction of the 365 g of HCl are formed in 10 minutes.
The speed of this reaction can be calculated by dividing the mass of the substance by time:
This speed can also be calculated as a function of the reagents.; for example, if 20 g of H were consumed2 in the same 10 minutes we have:
The units used in the examples may be other. Grams and minute can be replaced by liter and second. The important thing is that they are clearly defined and represented.
Factors that interfere with the speed of chemical reaction
The speed of a chemical reaction depends on several factors: gives contact surface between reagents, temperature, gives concentration of reactants and the presence of catalyst.
It is important to know the factors that influence the speed of chemical reactions so that they can be controlled. A very enlightening example is the way food is preserved, because its deterioration occurs through chemical reactions.
The larger the contact surface between reagents, the faster the reaction rate. Example: Effervescent antacids when crushed dissolve faster in water than in whole tablet form, because the contact surface becomes larger to react with water.
The higher the concentration of reagents, the faster the chemical reaction will be. This property is related to the number of collisions between particles. Example: A steel wool sample reacts faster with concentrated hydrochloric acid than with dilute hydrochloric acid.
Generally speaking, the higher the temperature, the faster the reaction proceeds. We can accelerate a slow reaction by subjecting the reagents to a higher temperature. Example: If we cook a food in a pressure cooker it will cook much faster due to the temperature rise compared to ordinary cookware.
Catalysts are substances capable of accelerating certain chemical reactions. Catalysts interact with the reactants, making the reaction between them easier to occur, causing an increase in product formation per unit time.
Due to these characteristics, catalysts are widely used in chemical industries, because the higher the reaction rate, the more efficient the process and the shorter the time taken to obtain a particular substance.
If we leave hydrogen peroxide (H2O2) in an open container, slowly a decomposition reaction will occur in water and oxygen:
However, if a platinum plate is introduced into the container, the reaction occurs much faster.