The Collision Theory of Chemical Reactions

2 Distinguish between reaction-producing molecular collisions and molecular collisions that do not yield reactions. 

If two molecules are to react chemically, it is reasonable to expect that they must come into contact with each other. What we see as a chemical reaction is the overall effect of a huge number of individual collisions between reacting particles. This view of chemical change is the collision theory of chemical reactions. 

Not all collisions result in a reaction in fact, most do not. If the colliding molecules do not have enough kinetic energy to break the bonds, the original molecules simply repel each other with the same identity they had before the collision (Fig. 18.1[b]). Sometimes they may have enough kinetic energy, but only sideswipe each 

Other and move off unchanged (Fig. 18.1 [c]). Other sufficiently energetic collisions may have an orientation that pushes atoms in the original molecules closer together rather than pulling them apart. 

To summarize For an individual collision to result in a reaction, the particles must have (1) enough kinetic energy and (2) the proper orientation. The rate of a particular reaction depends on the frequency of effective collisions. 

---

North, A. M. (1964) The Collision Theory of Chemical Reactions in Liquids. Methuen, London [3.3]. 

FIGURE 13.25 (a) In the collision theory of chemical reactions, reaction may take place only when two molecules collide with a kinetic energy at least equal to a minimum value, /rmn (which later we identify with the activation energy), (b) Otherwise, they simply bounce apart. 

A.M. North, The Collision Theory of Chemical Reaction in Liquids (Methuen, London 1964) H. Eyring, in Physical Chemistry, An Advanced Treatise, Vol. VII (H. Eyring et al. eds., Academic Press, New York 1975). 

The Collision Theory of Chemical Reactions Energy Changes During a Molecular Collision Conditions That Affect the Rate of a Chemical Reaction The Development of a Chemical Equilibrium Le Chatelier s Principle The Equilibrium Constant The Significance of the Value of K... 

According to the collision theory of chemical reactions, what two conditions must be satisfied if a molecular collision is to result in a reaction ... 

To gain insight into collisions in the gas phase, first we need to explore a model that can explain the properties of perfect gases. Then we consider the distribution of molecular speeds, a concept we previewed in Fundamentals F.2 and F.3. Finally, we define some of the parameters used in the collision theory of chemical reactions in the gas phase. 

Arrhenius established equation (20.22) by fitting experimental data into his equation. This was before the collision theory of chemical reactions had been developed, but his equation is consistent with the collision theory. In the preceding section, we discussed the importance of (1) the frequency of molecular collisions, (2) the fraction of collisions energetic enough to produce a reaction. 

---