Factors Affecting the Rate of Reactions

Introduction 

A chemical reaction takes place when two or more substances react with each other under specific conditions and form different substances known as products. The pace at which the chemical reaction takes place is known as the rate of a chemical reaction. If you’re looking to know the rate of reaction definition, it is defined as the speed at which the reactants in a reaction are converted into products. In other words, it is a time frame in which the reactants are directly converted into products, with or without the use of a catalyst. When the reaction takes place, multiple factors affect the rate of reactions (discussed below). There are different types of reactions in chemistry, some of which are sudden, whereas others take a longer period to complete. The difference in the period is the factor that affects the rate of reaction. Let’s now study each factor affecting the rate of chemical reaction in detail. 

Body

Concentration Of Reactants

First, the most important factor that influences the average rate of reaction is the concentration of the reactants. Both factors, that is, the concentration of reactants and the rate of reaction, are directly related to each other. 

Formula = rate (r) ∝ cn or r = kcn

Where r = rate of the chemical reaction 

c = concentration of the reactants 

n = order of reaction 

k = specific rate 

Explanation 

As the concentration of the reactants taking part in the chemical reaction increases, the number of collisions or activated collisions tends to increase. This, in turn, enhances the rate of a chemical reaction. This concept is based on collision theory, in which the collision increases due to the increase in concentration. Thus, we can say that the rate of reaction is directly proportional to the increase in concentration. 

 That is, rate of reaction ∝ collision frequency (Z) 

In addition to that, the rate of reaction decreases due to a decrease in concentration. And the decrease occurs in exponential form. 

Pressure 

In gaseous reactants, the concentration of the gases is increased with the increase in pressure. Thus, as discussed above, the increase in concentration increases the average rate of reaction. One thing to keep in mind is that pressure doesn’t affect the substances that are present in solid or liquid states. 

Explanation 

When the pressure in a particular gaseous system is increased, it directly enhances the number of collisions occurring between the reacting substances. This, in turn, affects the rate of the reaction in a positive way. This means the rate of reaction in which the reacting substances are present in gaseous form also increases. 

Temperature 

Temperature is the third among the factors affecting the rate of reactions. This is a little complicated to understand, as there are a few reactions in which the rate of reaction increases with the increase in temperature. In such reactions, the substances reacting gain kinetic energy and become more activated. This, in turn, increases the collision of the reacting substances, increasing the rate of a chemical reaction. However, this isn’t true in every case. The rate of biological reactions in which enzymes are used as a catalyst is known to decrease with the increase in temperature. The reason is that enzymes lose their functioning and activity due to an increase in temperature. 

Presence Of Catalyst 

Catalyst is a substance that helps the reaction to enhance the rate of the reaction. One thing to remember is that the catalyst itself doesn’t take part in the reaction. Meaning, it comes out the same as it was added. Catalyst is known to provide an alternative path for the reaction to take place. The new path has lower activation energy, meaning the reactants are easily shifted to products. In reversible reactions, catalysts play an important role. They are known to lower the activation energy of both forward and backward reactions. However, the catalysts are of two types – positive and negative. Positive catalysts are known to enhance the rate of reaction, whereas negative catalysts interfere with the reaction and decrease it. 

Nature of Reactants 

The nature of reactants is another factor affecting the rate of reactions. The two types of bonding – covalent and ionic compounds – are known to have different rates of reaction. Ionic compounds tend to react faster, enabling the rate of reaction to increase. Alternatively, covalent compounds are known to react slowly, enabling the rate of reaction to decrease. The reason is that in ionic compounds, there is only ion transfer taking place. But on the other side, covalent compounds have to undergo bond cleavage before they form products. 

Orientation of Reactants 

The rate of reaction depends on the orientation in which the reactants are reacting and forming products. If the reactants are present in the right orientation, it will lead to an increased rate of reaction. On the other hand, if the orientation of the reactant isn’t possible to attack, it will lead to a decrease in the rate of reaction. In other words, simple reactants have a higher rate of reaction as compared to complex ones because of the higher probability of proper orientation. 

Surface Area 

The surface area of the reactant is directly related to the increase in the rate of reaction. To increase the rate of reaction, the reactants and catalysts are used in finely powdered form. This increases the surface area of the reactants, which, in turn, increases the rate of reaction. For example, in zinc and hydrochloric reactions, the reaction speed increases when zinc is used in powder form as compared to when zinc is used in its zinc wire form. 

Intensity Of Light

The average rate of reaction is directly proportional to the intensity of light. When suitable light is used, the rate of photochemical reaction is increased. With the increase in the intensity of light, the number of photons also increases, which again increases the rate of reaction. 

Conclusion

So these were the factors affecting the rate of reactions. However, there is one more term that is related to the rate of reaction, the order of reactions. One of the most common types of reactions in which the rate of reaction depends on only one reactant is known as a first-order reaction. However, there are other order reactions – second-order reaction, third-order reaction, pseudo-first-order reaction, etc.