Rate of a Chemical Reaction

For any chemical reaction to take place, reactants are changed into products, under specific conditions such as optimum temperature, pressure, and in presence of some catalyst. For a complete understanding of the chemical reaction, it’s important to take into account the rate of a chemical reaction. It can be slow or fast, as per the nature of the reactants and the catalyst used. To understand it a little more, let’s take an example of a cellulose combustion reaction.  

Based on these factors, some of the chemical reactions can take place instantly whereas others take time to reach equilibrium. Combustion of wood is an example of fast reaction, while rusting of iron is an example of slow or lower rate of reaction. 

 Factors Affecting Rate Of Reaction 

Multiple factors determine the rate of a chemical reaction. Here are some examples:  

Nature Of Reaction 

The rate of reaction equation directly depends on the nature of the chemical reaction. Some reactions are instantaneous and others take a lot of time. The number, nature and size of reactants, and some other factors influence the rate of a chemical reaction too. If the reaction is complex, it will take more time compared with a simple reaction. The smaller the reactant, the faster the rate of reaction. The state of reactants also affects the rate of reaction. Gasses, for example, react faster than liquids or solids.

 Concentration 

To explain this, let’s revise collision theory. It states that the more concentrated the reactants, the faster the rate of reaction. The law of mass action indicates the same theory. Aside from the concentration, time is the major factor that influences the rate of a chemical reaction. 

 Pressure 

Pressure is the third factor that impacts the rate of a chemical reaction. Pressure is directly related to increasing the concentration of the reactants. 

Temperature

Again taking into account the collision theory, the chemical reaction that takes place at higher temperature releases higher energy because molecules of reactants move faster and collide with each other. Which, in turn, increases the rate of reaction. However, some reactions occur at specific rates and are independent of temperature. 

Presence Of Catalyst 

A catalyst is a substance that enhances the rate of reaction without taking part in the reaction. Reactions that possess lower activation energy use catalysts. It can easily increase the rate of reaction in both forward as well as reverse reactions. 

 Order Of Chemical Reaction 

The order of chemical reactions is directly related to the rate of a chemical reaction and the concentration of the reactants. In short terms, it is the sum of the power of the concentration of reactants. 

 Being an experimentally determined factor, the order of reaction can possess a fractional value too. However, by using the rate law, the order of reactions can be calculated. Here are a few possible values of the order of reactions. 

 Zero-order reactions: Reactions in which the concentration of reactants do not affect the rate of a chemical reaction have zero-order of reaction. 

• Negative integer: Reactions in which the concentration of the reactants is inversely proportional to the rate of a chemical reaction have negative order of the reaction. 
• Positive integer: Reactions in which the concentration of the reactants is directly proportional to the rate of a chemical reaction have positive order of the reaction. 
• Fractional value: Complex reactions have a fractional value of the order of reactions. 

 Order of reactions can be of different types

 Zero-order reactions: Reactions that don’t have any relationship between the concentration of the reactants and the rate of reaction. 

• First-order reaction: Reactions in which the rate of reaction will directly depend on only one reactant, regardless of how many reactants are present in it. 
• Second-order reaction: Reactions in which the rate of reaction will depend on two reactants. Or it can depend on the square of one reactant. 
• Third-order reaction: Reactions in which the rate of reaction will depend on three reactants. 
• Pseudo-first-order reaction: Reactions in which the rate of reaction appears to be first order, but it’s not is known as a pseudo-first-order reaction. 

 Conclusion

 Any chemical reaction has two main components: reactants and products. One thing to remember in a chemical reaction is the activation energy, which is the minimum amount of energy required to activate the reactants to participate in the reaction and form the products. As the reaction proceeds, the concentration of the reactants starts to decrease while the concentration of the products starts to increase.