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C7 A) Collision Theory
C7 A) Collision Theory
The rates of chemical reactions can be explained by collision theory. Collision theory states that the rate of chemical reactions is dependent on 3 variables that are split into two categories:
The 3 variables that affect the rate of reaction are temperature, concentration or pressure and surface area to volume ratio. When we look at how these 3 variables affect the rate of reaction, we need to make sure that we talk about the frequency of collisions between the particles. If one of the factors results in more collisions, we need to say, “more frequent collisions”, and if one of the factors results in less collisions, we need to say, “less frequent collisions”. This might seem a bit pedantic, but you will not get the mark if you say “more collisions”; you need to say “more frequent collisions”.
We are now going to look at the effect that temperature, concentration or pressure and surface area to volume ratio have on the rate of reaction.
- The frequency of collisions – this refers to how often the particles collide with one another. If there are more frequent collisions, there will be a greater rate of reaction. If there are less frequent collisions, there will be a lower rate of reaction.
- The energy transferred in a collision – particles will only react when there is enough energy to kick start the reaction. This is known as the activation energy and it is the minimum amount of energy needed to start a reaction. The energy is needed to break the bonds in the reactants.
The 3 variables that affect the rate of reaction are temperature, concentration or pressure and surface area to volume ratio. When we look at how these 3 variables affect the rate of reaction, we need to make sure that we talk about the frequency of collisions between the particles. If one of the factors results in more collisions, we need to say, “more frequent collisions”, and if one of the factors results in less collisions, we need to say, “less frequent collisions”. This might seem a bit pedantic, but you will not get the mark if you say “more collisions”; you need to say “more frequent collisions”.
We are now going to look at the effect that temperature, concentration or pressure and surface area to volume ratio have on the rate of reaction.
Temperature
A higher temperature gives the particles more kinetic energy. This means that the particles move around faster, which leads to more frequent collisions, thus increasing the rate of reaction. Also, as the particles have more energy due to the higher temperature, more energy will be transferred during a collision between the particles. This greater energy transferred between the particles during a collision is more likely to satisfy the activation energy, thus resulting in a reaction taking place (the activation energy is the amount of energy needed to start a reaction; if the activation energy is not met, a reaction will not take place).
So, a greater temperature leads to more frequent collisions and a greater energy transfer during collisions; both of these result in a greater rate of reaction.
A higher temperature gives the particles more kinetic energy. This means that the particles move around faster, which leads to more frequent collisions, thus increasing the rate of reaction. Also, as the particles have more energy due to the higher temperature, more energy will be transferred during a collision between the particles. This greater energy transferred between the particles during a collision is more likely to satisfy the activation energy, thus resulting in a reaction taking place (the activation energy is the amount of energy needed to start a reaction; if the activation energy is not met, a reaction will not take place).
So, a greater temperature leads to more frequent collisions and a greater energy transfer during collisions; both of these result in a greater rate of reaction.
Concentration & Pressure
If we increase the concentration of reactants in a solution, it means that there are more particles of the reactants in the same volume of water. This means that the particles are closer together, which results in more frequent collisions, therefore increasing the rate of reaction.
If we increase the concentration of reactants in a solution, it means that there are more particles of the reactants in the same volume of water. This means that the particles are closer together, which results in more frequent collisions, therefore increasing the rate of reaction.
We can increase the frequency of collisions in a gas by increasing the pressure of the gas. If we increase the pressure of a gas, it means that there are more particles in a given volume. This means that at a higher pressure, the particles are closer together, which results in more frequent collisions, thus increasing the rate of reaction.
Surface Area to Volume Ratio
We can increase the rate of reaction by breaking up the reactants into smaller pieces. When we break the reactants up into smaller pieces, the surface area to volume ratio of the reactants increases. This means that there is a greater surface area on the reactants for the particles to collide upon, which leads to more frequent collisions, thus increasing the rate of reaction.
We can increase the rate of reaction by breaking up the reactants into smaller pieces. When we break the reactants up into smaller pieces, the surface area to volume ratio of the reactants increases. This means that there is a greater surface area on the reactants for the particles to collide upon, which leads to more frequent collisions, thus increasing the rate of reaction.
Final Point
So, the rate of reaction depends on the frequency of collisions and the energy transferred in a collision. All three of the factors (temperature, concentration or pressure and SA to Vol ratio) influence the frequency of collisions. Temperature is the only factor that affects the energy transferred in a collision.
So, the rate of reaction depends on the frequency of collisions and the energy transferred in a collision. All three of the factors (temperature, concentration or pressure and SA to Vol ratio) influence the frequency of collisions. Temperature is the only factor that affects the energy transferred in a collision.