Collision Theory: Molecular Collision, Surface Area Types, Examples

Collision theory explains why reactions occur at varying rates and suggests how to adjust a reaction's rate. Collision theory is a mathematical model for predicting the speeds of chemical reactions, especially in gases. 

Collision theory assumes that in order for a reaction to occur, the reacting species (atoms or molecules) must come together or collide with one another.

Key Takeaways: Collision theory, molecular collision, bimolecular gas-phase reaction, collision theory equation, chemical kinetics, the surface area of the collision theory.

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Collision Theory

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The chemical process is dependent on collisions between distinct atoms in molecules, and all of the particles must collide in order for the collision to occur. In addition, collision is primarily determined by two factors: kinetic energy and the orientation of bonds that are meant to be formed between distinct molecules of chemical compounds. 

The term "collision" refers to when particles or molecules collide with one another. According to collision theory, chemical reactions occur when particles collide (strike) one other. In addition, reactant-molecule collision is required, however this may not be sufficient for the chemical reaction. 

After the chemical process, molecule collision must be sufficient to obtain the desired products. The features and attributes of the resulting product, on the other hand, will be determined by how well the collision process works. In order to understand and determine the subsequent products, it is necessary to first understand the collision theory.

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Collision Theory: Molecular Collision

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• It is a simple rule that the more molecules there are, the more collisions there will be. As a result, the proportion of collisions varies on the number of particles involved in the collision.
• The collision of molecules is required prior to their chemical reaction.
• Collisions should have enough kinetic energy to start a reaction between them. Only if the collision strength is strong enough will the bond be disrupted.
• Collisions are influenced by temperature; the higher the temperature, the more collisions. At greater temperatures, collisions are more violent.
• Because neutral molecules have a lower energy level, they can't break any bonds or participate in the collision process; however, molecules with adequate energy can.
• Bending, stretching, and twisting the bond are all part of the reaction process. As a result, energetic molecules are required for the process.

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Collision Theory Explanation

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Collision theory refers to the research or assumptions made about molecules or particles that may collide in chemical reactions to produce desired chemical products. For the chemical reaction, however, not all collisions are repaired. Only bonds will be broken if the energy of particles or molecules is greater than or equal to activated energy. 

The orientation of particles must be appropriate according to the chemical process for proper bond and molecule rearrangement. The chemical theory, on the other hand, is not applicable to all elements because it requires collision frequency calculations. Only gaseous elements can be accurately estimated in terms of collision frequency. As a result, according to the collision theory explanation, collision theory can only be used for gas-phase chemical reactions.

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Surface Area of Collision Theory

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There are more molecules on the surface when the surface area is large, and more molecules can react with each other, resulting in a higher collision or reaction rate. As a result, the larger the surface area, the faster the reaction will be. Furthermore, according to the collision theory, bigger surface areas of molecules have more energy, which raises reaction speeds.

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Collision Theory: Real Life Examples 

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The Cricket Bat is reactant A in the diagram below, whereas the ball is reactant B. As a result, when a ball collides with the boundary, it is considered a better collision. A failed attempt occurs when the ball does not cross the boundary line. Let's have a look at the various scenarios that this example could lead to:

Scenario 1

The batsman may not be able to hit the ball if the bowler throws a fastball in the middle of the pitch. As a result, the batsman will entirely miss the ball.

Scenario 2

When the bowler throws an off-speed ball, the batsman checks the ball's swing. In this condition, the batsman is unable to properly heat the ball, and the bat may lightly contact the ball, resulting in an unsuccessful attempt.

Scenario 3

The bowler throws a curveball that appears to be destined for the pitch's outside corner. The hitter swings with all his might, but his bat grazes the ball's underbelly, skewing the ball to the right and into the crowd. “Foul ball, still two strikes!” shouts the umpire.

Scenario 4

When the bowler produces a down-the-middle pitch, the batsman has the ability to hit the ball accurately and with maximum strength. In this situation, the ball may cross the boundary line in the air and be caught by a member of the stadium crowd. It can now be a six!

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Collision Theory: Bimolecular Gas Phase Reaction

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According to collision theory, the rate of a bimolecular gas-phase reaction is given below:

Where

• k = rate constant in number of molecules^-1s^-1m³ 
• nA = Number of density of A in the gas in m^-3
• nB = Number of density of B in the gas in m^-3
• Z = Collision frequency in s^-1m^-3
• ρ = steric factor
• Ea = activation energy of the reaction in J mol^-1
• T = temperature in Kelvin
• R = Gas constant in J mol^-1K^-1

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Collision Theory: Arrhenius Equation

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where A = Arrhenius factor

Ea = activation energy

T = temperature 

R = Gas constant

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Things to Remember

Collision theory is a mathematical model for predicting the speeds of chemical reactions, especially in gases.

• Collision theory works on the assumption that for a reaction to occur, the atoms/molecules (reacting species) must come together or collide with one another. 
• However, not all collisions result in chemical change. Only if the species brought together have a minimum value of internal energy equal to the reaction's activation energy would a collision be effective in creating chemical change.
• Furthermore, the colliding species must be orientated in a way that allows for the essential atom and electron rearrangement.
• The pace of a chemical reaction is equal to the frequency of effective collisions, according to the collision theory. Because atomic or molecular collision frequencies can only be estimated with some accuracy for gases (using the kinetic theory), the collision theory's use is confined to gas-phase reactions.

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