Question Video: Recalling How Parameters in Collision Theory Affect Reaction Rate Chemistry • Third Year of Secondary School

Video Transcript

Which one of the following would not increase the rate of a reaction, according to collision theory? A) Particles colliding more frequently. B) Particles having more energy. C) A higher temperature. D) A higher activation energy. Or E) a higher particle concentration.

Collision theory is a theory that relates particles in the collisions with their reactivity and states that reactions happen when particles collide with sufficient energy. More frequent and higher energy collisions increase the rate of the reaction. So, what collision theory says is that reactions only happen because of a collision. But when a collision does occur, one of two things will happen. What will happen will depend on two factors, the energy of the particle collision and the activation energy of the reaction.

In the energy–reaction progress diagram, we can see the activation energy as the hump between the reactants and the products. The value of the activation energy is equal to the height of this bump above its nearest baseline. If the energy of the collision is greater than the activation energy, collision theory states that a reaction will occur. But if the energy of the collision is less than the activation energy, the particles will simply bounce off one another. In simplest terms, the activation energy is the energy needed to break the bonds in the reactants and allow the products to form.

Now that we’ve recapped on collision theory, we can have a look at the question and find which statement would not increase the rate of a reaction, according to collision theory. The first statement is, particles colliding more frequently. According to collision theory, the more frequent the collisions, the higher the reaction rate. This is because the more collisions there are, the more opportunities there are for reactions to occur. Since this would increase the rate of a reaction, it’s not a correct answer.

What about particles having more energy? Well, the more energy the particles have, the greater the energy of the collisions, which means more of the collisions will lead to a successful reaction. Since this would also increase the reaction rate, it’s also an incorrect answer.

So, what about a higher temperature. This can be tied back to the previous statement, because the particle energy increases with temperature. So, a higher temperature would mean higher energy collisions and more reactions.

So, we can move on to the fourth statement, a higher activation energy. Having a higher activation energy means that each individual collision needs to have a higher energy in order for a successful reaction to occur. So, a higher activation energy will slow the reaction down and, therefore, decrease the rate of the reaction. So, we’ve found the correct answer.

But just to be safe, let’s have a look at the fifth statement. A higher particle concentration will mean that particles will collide more frequently. More frequent collisions means a higher reaction rate. So, this too is not a correct answer. So, of the five statements given, the only one that would not increase the rate of reaction, according to collision theory, is a higher activation energy.