Collision Theory

What Is Collision Theory?

The chemical reaction depends upon the collision between different atoms of the molecules, and all the particles must collide with each other to get the result of the collision. Furthermore, collision depends upon mainly two factors like kinetic energy and orientation of bonds that are supposed to be created between different molecules of the chemical compounds. Let us study the collision theory for a better understanding of the chemical reactions of different compounds. 

Collision word indicates that particles or molecules with hit one another or collide. So, collision theory says that when particles collide (hit) each other, chemical reaction takes place. Furthermore, reactant molecules collision is a must, but this may not that much enough for the chemical reaction. Molecules collision must be sufficient to get the desired products after the chemical reaction. Well, the resultant product’s features and properties will depend upon the effective collision process. So, this would be essential to understand the collision theory to understand and determine the resultant products.

Molecular Collisions: Collision Theory

As it is a straightforward rule that more molecules lead to more collisions. So, the proportion of collision depends upon the number of particles that will participate in the collision.

The collision of molecules is essential before the chemical reaction between them.

Collisions should have adequate kinetic energy that can initiate the reaction between them. Bond disruption will be done only if the strength of the collision is high.

Collision depends upon the temperature—higher the temperature, higher the collisions. Collisions are vigorous in higher temperatures.

Neutral molecules have less energy level, and hence they can not break any bonds or participate in the collision process, but molecules having enough energy will participate in the collision.

The reaction process involves bend, stretch, and distorting bond. So, the reaction needs energetic molecules.

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Image showing Molecules Collision Theory

Collision Theory Explanation

Collision theory includes the studies or assumptions of molecules or particles that may participate in collision in chemical reactions that give desired chemical products as a result. However, all collisions are not mended for the chemical reaction. If the energy of particles or molecules is more than or equivalent to activated energy, then only bonds will be broken. For the proper rearrangement of bonds and molecules place, the orientation of particles must be suitable according to the chemical reaction. Well, the chemical theory is not for all types of elements as it involves the calculations of collision frequencies. Accurate estimation of collision frequency is possible only for gaseous elements. So, the collision theory explanation states that you can apply collision theory only for gas-phase chemical reactions.

Collision Theory Surface Area

Whenever the surface area is extensive, there are more molecules on the surface, and more molecules can react with each other resulting in higher collision or reaction rate. So, it is noted that the larger surface area will increase the rate of reaction. Furthermore, if the surface area of molecules is higher have more energy, and it also increases the reaction rates according to the collision theory. 

Collision Theory Examples

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Ball And Bat: Explanation of Collision Theory

In the below figure, the Cricket bat is reactant A and ball is reactant B. So when a ball hits the boundary, it is said to be a better collision. When the ball does not hit the boundary line, it is a failed attempt. Here let’s discuss the different situations concerning this example.

Scenario 1:

When the bowler throw fastball in the pitch’s middle, the batsman may not be able to hit the ball. So, the batsman will miss the ball completely.

Scenario 2:

Batsman checks the ball’s swing when the bowler throws the off-speed ball. In this situation, the batsman can not heat the ball properly, and the bat may contact the ball slightly, and it will be considered as a failed attempt.

Scenario 3:

If the ball is bowled curved, it may be staying out of the pitch’s corner. The batsman can not hit the ball accurately even in this situation because of a foul ball.

Scenario 4: 

When the bowler throws the ball that delivers down the middle pitch, the batsman can hit the ball accurately with the fullest strength. In this case, the ball may cross the boundary line through the air, and someone from the audience in the stadium can catch it. It can be a six now!


Types of Collision Theory

Elastic collision: In some collisions, the system’s both kinetic and momentum energy are conserved are called an elastic accident. Here, the collision between different subatomic particles is mostly elastic. For example, two glass or steel balls’ collision is generally elastic. The nature of the forces involving inelastic collisions is conservative. 

Inelastic collision: In some collisions, kinetic energy is not conserved, and the only momentum is conserved is said to be an inelastic collision. Every day we can find many collisions in daily life that are mostly inelastic. 

Solved Example


Suppose, the activation energy required for the reaction between molecules of hydrogen and iron, 2HI(g) → H2 + I2(g) is 209.5 kJ mol-1 at 581 K. Find the reactants fraction of particles of having energy greater than or equal to activation energy?


Ea = 209.5 kJ mol - 1 = 209500 J mol - 1

T = 581 K

R = 8.314 JK - 1 mol - 1

The fraction of molecules of reactants having energy equal to or greater than activation energy is as follows:

x = e-Ea/RT

ln x = -Ea/RT

log x = Ea/2.303RT

log x = 209500 J mol-1/2.303 X 8.314 J K-1 mol-1 X 581 = 18.8323

x = antilog (18.323)

= antilog 19.1977

= 1.471 X 10-19

FAQ (Frequently Asked Questions)

1. What are the factors the collision rate or reaction rate?

Collision theory is generally for gaseous chemical reactions. Many factors are there that affect the chemical reaction. Some essential factors are listed below:

  • The pressure

  • The temperature

  • Surface Area

  • Particles quantity

  • The energy of the particle

2 .Why higher temperature increases the reaction rates according to the collision theory?

When the temperature of molecules is higher, the movement and energy of molecules will increase. So, the frequency of collision will also increase and that lead to a possible collision. Thus, higher temperature lead to an effective collision and increased reaction rates.