28 November 2023

In the evaluation and understanding of the chemical processes that occur in the environment, on the planet and in everyday life, the speed of chemical reactions it is a key factor. This chemical reaction process allows us to understand what factors affect the speed of a reaction and how it can be modified to adjust it according to the needs and/or requirements.

Concept and definition of reaction rate

The reaction rate is a metric indicating speed with which the products are generated from the reactants. In some cases, this can happen instantly just on contact, seen in things like explosions.

There are chemical transformations that have a very low speed and take years to complete, while most occur at an intermediate rate. The speed of a chemical reaction indicates the time when they occur products or reactants disappear.

This can be measured through the variation in the concentration of the reactants or products during the process, and the amount of substance. These experience a transformation into a reaction per unit of volume and time. For example, the combustion of gas is much faster than the reaction of a material such as metal, which can take years.

The analysis of the changes produced through this process is the responsibility of chemical kinetics, a discipline specialized in studying the speed of reactions, based on kinetic energy. It also explains how versatile conditions modify the rate of reaction of a material or substance.

Chemical kinetics is responsible for the analysis of the evolution of a process, while chemical dynamics focuses on the study of speed of different types of reactions. This refers to the degradation in the amount of reactants or products in a given interval of time, which allows calculating their average speed.

The importance of reaction speed can be understood in everyday situations, such as the expiration date of processed foods, which indicates until when product quality is guaranteed. In industrial processes, such as the manufacture of ammonia, the speed of the reaction is essential to achieve higher production in less time.

What is the formula for reaction rate in chemistry?

It can be defined as the amount of reactants that are degraded or products formed per unit of time. This is commonly expressed in mol/l × s.

During a chemical reaction, the concentration of the reactants decreases as the corresponding products are formed. This change can be observed by the reduction of the concentration of the reactants or the increase in the concentration of the products. To analyze the concentration in a chemical process, the mole fraction (Frac) is used, which measures the proportion of a substance in relation to the total moles of the solution.

  • Chemical reaction: Br2 (aq) + H – COOH (aq) ® 2 HBr (aq) + CO2 (g).

The rate of a chemical reaction is determined by the calculation of the variation of the concentration of reactants and products as a function of time. If the case is that a product is selected, the term to use is the velocity with a positive sign, since the variation of the concentration is always positive. If the selected reagent is Br2, its decay rate is reflected with a negative sign.

The Law of Rate explains how the rate of a chemical reaction It is related to the concentration of the reactants present in the reaction. In the case of the reaction aA (products), the Rate Law is expressed as velocity = k(A)ⁿwhere ‘what‘ is a constant of proportionality called the rate constant and ‘no‘ which is the order of the reaction with respect to ‘TO‘.

What factors affect the rate of chemical reaction?

The chemical reaction rate can be altered by different variables that can be manipulated to obtain specific results, such as speeding up or slowing down the reactions. These factors are what determine the frequency or speed of collisions and the energy of the particles. Any element that influences these two variables alters the reaction rate by exerting pressure.

How can you change the rate of a chemical reaction?

Altering the rate of chemical reactions depends, in itself, on four factorswhich are the ones that influence these variables:

  • Division of reagents.
  • Reagent concentration.
  • Temperature.
  • Addition of catalysts.

To generate a result, the particles they must collide correctly and with enough energy, because its movement does not stop and its direction cannot be controlled, but there are factors or states that can.

It is important to note that gases, pressure, volume, and number of particles are interrelated, so if you want to increase the pressure of a gas keeping its number of particles constant, it is necessary to decrease the volume of the container that contains it.

When the volume of a gas is reduced, the gas particles have less room to move, which increases the frequency of collisions between the particles and the walls of the container, and as a result gas pressure rises. The factors to take into account in this process are detailed below:

  • Physical state of the reactants: It is an important factor influencing the rate of a chemical reaction. The reactions involving ions in solution they have a much faster speed compared to those that require breaking covalent bonds. In the heterogeneous reactionsthe speed also depends on the state of division of the reactants, since the contact surface between the phases directly affects the reaction speed, therefore a greater division of the reactant increases the contact surface between the phases and favors a higher speed. of reaction.
  • The concentration of the reactants: It is a key factor that influences the speed of a chemical reaction, since by altering the concentrations, it is possible to increase the rate of the reaction.
  • Temperature: As thermal energy increases, the speed of collisions between molecules increases, which usually result in increased speed of reaction.
  • The catalysts: They are substances that speed up the rate of a chemical reaction without being consumed in the reaction itself, although they do not affect the stable equilibrium state. A type of biological catalyst is the enzyme, which increases the speed of a chemical reaction in living things.

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