The collision theory

We are going to look in detail at reactions which involve a collision between two species. For an endothermic change, the products would have a higher energy than the reactants, and so the green arrow would be pointing upwards. The area under the curve is a measure of the total number of particles present.

The two simply bounce off each other. In any system, the particles present will have a very wide range of energies. For gases, this can be shown on a graph called the Maxwell-Boltzmann Distribution which is a plot of the number of particles having each particular energy. The only difference if the reaction was endothermic would be the relative positions of the reactants and products lines.

The reaction can only happen if the hydrogen end of the H-Cl bond approaches the carbon-carbon double bond. Reactions involving collisions between more than two species are going to be extremely uncommon see below.

Reactions involving collisions between two species It is pretty obvious that if you have a situation involving two species they can only react together if they come into contact with each other. You can show this on an energy profile for the reaction. Activation energy is involved in breaking some of the original bonds.

These react to give chloroethane. Activation energy is the minimum energy required before a reaction can occur. We can mark the activation energy on the Maxwell-Boltzmann distribution: You could either go straight to these pages if you are interested, or access them later via the rates of reaction menu link at the bottom of the page.

A hydrogen atom gets attached to one of the carbons and a chlorine atom to the other. This might help you to understand why the orientation of the two molecules is so important. To enable them to react we either have to change the shape of the curve, or move the activation energy further to the left.

All three or more particles would have to arrive at exactly the same point in space at the same time, with everything lined up exactly right, and having enough energy to react. They first have to collide, and then they may react.

Collision theory

The approaching chlorine atom is also slightly negative because it is more electronegative than hydrogen. Questions to test your understanding If this is the first set of questions you have done, please read the introductory page before you start. The Maxwell-Boltzmann Distribution and activation energy Remember that for a reaction to happen, particles must collide with energies equal to or greater than the activation energy for the reaction.

As a result of the collision between the two molecules, the double bond between the two carbons is converted into a single bond. You can get at these via the rates of reaction menu - there is a link at the bottom of the page. You can change the shape of the curve by changing the temperature of the reaction.

The Maxwell-Boltzmann Distribution Because of the key role of activation energy in deciding whether a collision will result in a reaction, it would obviously be useful to know what sort of proportion of the particles present have high enough energies to react when they collide.

This is a useful term which covers any sort of particle you like - molecule, ion, or free radical. Use the BACK button on your browser to return to this page. It concentrates on the key things which decide whether a particular collision will result in a reaction - in particular, the energy of the collision, and whether or not the molecules hit each other the right way around the orientation of the collision.

For a simple over-all exothermic reaction, the energy profile looks like this: It makes no difference to the discussion about the activation energy.The collision theory says that when particles of the reactant hit each other, only a small percentage of the collisions will cause a chemical change.

This is why reaction rates.

Collision Theory

A collision that meets these two criteria, and that results in a chemical reaction, is known as a successful collision or an effective collision. Collision theory explanation Collision theory provides an explanation for how particles interact to cause a reaction and the formation of new products.

Collision theory: Collision theory, theory used to predict the rates of chemical reactions, particularly for gases.

The collision theory is based on the assumption that for a reaction to occur it is necessary for the reacting species (atoms or molecules) to come together or collide with one another. This page describes the collision theory of reaction rates. It concentrates on the key things which decide whether a particular collision will result in a reaction - in particular, the energy of the collision, and whether or not the molecules hit each other the right way around (the orientation of.

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The collision theory
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