Collision Theory - Online Tutor, Practice Problems & Exam Prep

In chemical reactions, the rate at which reactants transform into products is significantly influenced by molecular collisions. Factors such as temperature, activation energy, concentration of reactants, and molecular orientation play crucial roles in determining the success of these collisions. A higher temperature increases the energy of collisions, while a lower activation energy and higher concentration of reactants lead to a greater frequency of collisions, thus enhancing the reaction rate. Proper orientation, dictated by molecular shape, is essential for effective collisions. The Arrhenius equation,

$K=A\cdot e^{-\frac{Ea}{RT}}$

where K is the rate constant, A is the frequency factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin, quantifies these effects. A higher K value signifies a faster reaction rate. Additionally, the frequency factor A is composed of the orientation factor (P) and the collision frequency (Z), with P representing the fraction of collisions with correct orientation and Z representing the frequency of molecular collisions. Understanding these principles is key to manipulating and predicting reaction rates.

Collision Theory Concept 1

According to collision theory, a chemical reaction is successful when two energetic reactants successfully collide. And when we talk about successfully collide, we're going to say that for successful collisions, reactive molecules must collide with enough energy so they have to hit each other hard enough and with proper orientation, so they have to hit each other in the right spots for them to stick together.

Now, what are the factors that are influencing our collisions? Well, the first factor is temperature. We're going to say here if we can increase the temperature of our reaction then this can help increase the number of energetic collisions. More energetic collisions, more success in possibly connecting together between reactive molecules.

Now activation energy. If we can ensure that our chemical reaction has a low activation energy then this will also increase our rate of reaction. Next, concentration of reactants. If you can increase the amount of reacting concentrations, that means they're going to be more reacting molecules floating around, which will increase their frequencies of collision. Increasing the frequencies of collisions mean that they bump into each other more often, and that increases the possibility of some of them sticking together.

Now four, we're going to talk about orientation. This is pretty self-explanatory. Here we say molecules must collide with proper orientation, and if they do so, that'll equal a successful collision. Now here proper orientation is partially determined by the shape of molecules, so for them to connect in the right spots, the molecules themselves have to have ideal shapes with one another.

Now the rate of reaction is influenced by molecular collisions. Here we're going to say that if we can increase the number of overall collisions, then this can result in a faster rate of reaction. So now keep all of these factors in mind when we're talking about successful collisions, which in turn will lead to a faster rate of reaction.

Collision Theory Example 1

In this example question, it says for chemical reaction to occur, all the following must happen except. All right. So here a large number of collisions must occur. Chemical bonds and reactants must break. Reactant molecules must collide with correct orientation, Reactant molecules must collide with enough energy or none of the above.

All right, so let's make sure we take out the ones that we know have to happen. So here reactive molecules must collide with correct orientation. This is one of the foundations of collision theory we talked about. They have to basically connect in the right spots. So here this has to happen. What else must happen? Reactive molecules must collide with sufficient energy. Enough energy.

Now here we have AB and E. So for B we say chemical bonds in reactants must break. Well, the whole point of these chemical reactions is to change reactants into products, and reactants can only change into products if their bonds break. So B has to happen. The answer here is A. Yes, collisions need to occur for them to stick together, but it's not necessary that it has to be a large enough number of collisions.

Some reactions can happen with just a few collisions because they're highly favorable. So here A would be the best answer. We need collisions. We don't always necessarily need a large number of collisions. Again, some reactions only need a few and they automatically stick together, right? So here the final answer would be option A.

Collision Theory Concept 2

Now the Arena's equation illustrates how the rate of a reaction is affected by different variables. Now we're going to say here that a faster reaction rate would have a high K value or rate constant K, it would have a higher a variable, it would have a lower activation energy, and it would have a higher temperature.

Now here we can incorporate these variables into our Arrhenius equation itself. In the Arrhenius equation we say that K, which represents your rate constant equals A which represents your frequency factor times the inverse of the natural log to be negative EA over RT. Now here EA is our activation energy. R here represents our gas constant which is 8.314 Joules over moles times K which is Kelvin and then here T equals temperature in Kelvin.

With this radius equation Arrhenius equation we can say here that the higher the rate constant K than the higher the rate of reaction or the faster the rate of reaction. Now with our frequency factor A, we can say that it is split into two other variables, and those variables are the orientation factor, which uses the variable P and the collision frequency, which is using the variable Z.

Now we can say here that our orientation factor P it's just a number that represents the fractions of collisions with correct orientation. Here we can say that the larger the reacting molecules or reactants, then the lower the orientation factor, and the lower the orientation factor, the less successful your collision will be. With the collision frequency Z, that's just a frequency of molecular collisions that occur. So the higher your Z value, the more molecular collision that can occur, the more likely some of them will be successful.

So just keep in mind these basic ideas and principles. When it comes to the Arrhenius equation, it's really just looking at how all the factors together can result in either a successful or unsuccessful reaction.

K = A ⁢ e - E A R T

Collision Theory Example 2

Determine which of the following reactions has the smallest orientation factor which uses the variable P. Now remember when it comes to the orientation factor, we say that the larger the reactant molecules then the smaller your orientation factor will be.

So if we take a look here in A our reactant molecules are just this iodine and then HI. For B it's just two hydrogens. Now for sure this is out because hydrogens are the smallest element. So this one will be expected to have a very high orientation factor.

For C we have BR₂ with this molecule which is called ethene and here we're not concerned with the products being formed. Again, we're looking at the size of the reacting molecules, so our reactants and if we take a look here, we know that these also out because the reactants are not all the same size, so they wouldn't have the same orientation factor values.

The answer here is option C because BR₂ and ethene are definitely larger in size than just an iodine by itself. And HI. So here for C those two reacting molecules are the largest. This will result in smaller orientation factors which could result in an unsuccessful collision later down the road, so you might be less likely to form the product here as a result.

So keep this in mind when we're talking about the orientation factor. Larger reactants equals smaller orientation factor.

Here’s what students ask on this topic:

What is collision theory?

Collision theory is a scientific concept that explains how chemical reactions occur and why reaction rates differ for different reactions. According to this theory, for a reaction to take place, the reactant particles (atoms, molecules, or ions) must collide with one another. However, not all collisions result in a reaction. For a successful reaction to occur, two criteria must be met:

1. The reactants must collide with sufficient energy to overcome the activation energy barrier, which is the minimum energy required to break the bonds of the reactants and form new bonds for the products. This energy is known as the activation energy.
2. The reactants must collide with the proper orientation that allows the atoms to rearrange and form new bonds to produce the reaction products.

The collision theory helps us understand why certain factors, such as temperature, concentration, surface area, and the presence of a catalyst, affect the rate of a reaction. For example, increasing the temperature increases the energy of the particles, which leads to more collisions and a higher chance of successful collisions, thereby increasing the reaction rate.

Which statement best applies collision theory to the prevention of a dangerous reaction from occurring?

Collision theory explains how chemical reactions occur and what factors affect their rates. According to this theory, for a reaction to take place, reactant particles must collide with sufficient energy, known as the activation energy, and with the correct orientation.

To prevent a dangerous reaction from occurring, you can apply collision theory by manipulating the conditions to make collisions less likely or less effective. This could involve lowering the temperature, which decreases the kinetic energy of the particles, thus reducing the number of collisions with enough energy to surpass the activation energy. Another method is to decrease the concentration of reactants, which reduces the frequency of collisions. Additionally, you can remove or not add a catalyst that would otherwise lower the activation energy required for the reaction. By controlling these factors, you can effectively prevent or slow down a potentially dangerous reaction according to the principles of collision theory.

According to the collision theory, what is required for a high number of effective collisions?

According to the collision theory, for a high number of effective collisions to occur, several factors must be present. Firstly, the reacting particles must collide with sufficient energy to overcome the activation energy barrier; this is known as the energy criterion. The activation energy is the minimum energy required for a reaction to occur. Secondly, the particles must have the correct orientation when they collide, which is the orientation criterion. This means that the particles must align in a way that allows for the proper rearrangement of atoms and the formation of new bonds.

In practical terms, increasing the concentration of reactants will generally lead to more collisions per unit time, thus increasing the likelihood of effective collisions. Similarly, increasing the temperature of the system will increase the kinetic energy of the particles, leading to more collisions with energy greater than the activation energy. Finally, the presence of a catalyst can lower the activation energy barrier and provide an alternative pathway for the reaction, thereby increasing the number of effective collisions.

Which theory applies to the collision theory?

The collision theory applies to chemical kinetics, which is the study of the rates at which chemical reactions occur. According to this theory, for a reaction to take place, the reactant particles must collide with each other. However, not all collisions result in a reaction. For a successful reaction to occur, two main criteria must be met:

1. The particles must collide with sufficient energy to overcome the activation energy barrier. This minimum energy required for a reaction is known as the activation energy.
2. The particles must have the correct orientation during the collision to allow the necessary rearrangement of atoms and electrons to form the products.

The collision theory helps explain why certain factors, such as temperature, concentration, surface area, and the presence of a catalyst, affect the rate of a reaction. For instance, increasing the temperature increases the kinetic energy of the particles, leading to more frequent and more energetic collisions, thus increasing the rate of reaction.

According to the collision theory, what is required for a high number of effective collisions?

According to the collision theory, for a high number of effective collisions to occur, certain conditions must be met. First, the reacting particles must collide with each other. Second, they must collide with sufficient energy to overcome the activation energy barrier; this is known as the energy criterion. The activation energy is the minimum amount of energy required for a reaction to occur. Third, the particles must have the correct orientation when they collide, so that the atoms that need to react are in proximity to each other; this is the orientation criterion. When both the energy and the orientation criteria are met, a collision can result in a chemical reaction, and it is termed an effective collision. Factors such as increasing temperature, concentration of reactants, surface area, and the use of a catalyst can increase the number of effective collisions, thus increasing the rate of reaction.