Collision Theory - Video Tutorials & Practice Problems
Get help from an AI Tutor
Ask a question to get started.
According to Collision Theory:chemical reaction is successful when 2 energetic reactants successfully collide.
Understanding Collision Theory
1
concept
Collision Theory Concept 1
Video duration:
2m
Play a video:
According to collision theory, a chemical reaction is successful when 2 energetic reactants successfully collide. And when we talk about successfully collide, we're gonna say that for successful collisions, reactant 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 gonna 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 reacting 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 reactant concentrations, means there are gonna 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, 4, we're gonna 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.
A chemical reaction is successful if reactant molecules can combine together to form a new product.
2
example
Collision Theory Example 1
Video duration:
1m
Play a video:
In this example question, it says for chemical reaction to occur, all the following must happen except alright. So here a large number of collisions must occur, Chemical bonds in reactants must break. Reactant molecules must collide with correct orientation. Reactant molecules must collide with enough energy or none of the above. Alright. 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? Reactant molecules must collide with sufficient energy, enough energy. Now here we have a, b, 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.
3
concept
Collision Theory Concept 2
Video duration:
2m
Play a video:
Now the Arrhenius 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 e a over r t. Now here e a 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 Arrhenius equation or Arrhenius equation, we can say here that the higher the rate constant k, then 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 2 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.
Frequency Factor is made up of 2 variables:
1. Orientation Factor (p)
2. Collision Frequency (z)
4
example
Collision Theory Example 2
Video duration:
1m
Play a video:
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 2 hydrogens. Now for sure this is out because hydrogens are the smallest element. So this will be expected to have a very high orientation factor. For c, we have b r 2 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 d is 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 b r 2 and ethene are definitely larger in size than just an iodine by itself and HI. So here, for c, those 2 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 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.