collision theory

Question 1

collision theory

Answer 1

• it explains rates on the molecular level, before molecules can react, they must collide.
• Not all collisions results in a chemical reaction.
• Successful collisions result in a chemical reaction.

Question 2

Succesful collision-
In summary

Answer 2

• molecules must collide with sufficient energy, known as the activation energy, so that chemical bonds can break.
• molecules must** collide** with proper orientation to keep Ea as low as possible.
• • A collision that meets these two criteria, and that results in a chemical reaction, is known as a succesful collision or an effective collision.*

Question 3

Factors affecting rate of reaction: nature of the reactants

Answer 3

• Reactions will proceed differently depending on which substances are reacting.
• Ions in solution tend to react quickly and almost instantaneously in percipitate reactions.
• The more mobile the reactant particles are the faster the reaction rate.
• Reactions rates tend to decrease in moelcules with strong covalent bonds, especially, if the molecules are large.

Question 4

The concentration of the reactants

Answer 4

• according to the particle theory for matter, two particles must approach each other to react together.
• So, chemical reactions must depend on the collisions between the particles of reactants.
• The “collision theory” relies on this to explain the rate of chemical reaction.
• As the concentration of reactants increases, the number of particles of reactants, per uniti of volume increases; the number of collisions per second also increases
• –> The rate of reaction will increase. The opposite is also true; a decrease in concentration will cause a decrease in reaction rate.

Question 5

the surface area of the reactants

Answer 5

• all chemical reactions occur on the surface of the reactants. If one of the reactants is broken down into smaller pieces, the total surface area which can react with the other reactant(s) increases.
• The number of collisions between the particles of reactants increases and the rate of reaction also increases.

Question 6

1

Temperature

Answer 6

• High temperature create faster speeds in the molecules comprising the reactants; this causes particles to collide with more force (or higher kinetic energies), causing increased probalities of a chemical reaction occuring for that collision.
• Dissolving sugar in a glass of cold water, versus a cup of hot coffee; it will dissolve quicker in the hot coffee.

Question 7

2

Temperature

Answer 7

• Thus, the rate of reaction is usually higher at higher temperatures, and the rate is reduced as temperature decreases, which is why we use refrigerators – to slow down the chemical reactions which spoil food.
• Temperature also *causes particles to collide with more possible orientations and by increasing the randomness of collisions, it increases the chance of more correct alignments, *and therefore, more succesful collisions.

Question 8

Pressure

Answer 8

• An increase in the overall pressure will cause an increase in the number of collisions between the particles of reactant, accelerating the rate of chemical reaction, and vice-versa for a decrease of the over pressure on the system.
• –> This only applies to reactions in which the reactants are gases.

Question 9

1

Effect of a Catalyst

Answer 9

• a catalyst is a bustance that alters the rate of a chemical reaction without itself undergoing any permanent chemical change.
• There are two importants limits regarding the actions of a catalyst:
• a catalyst does not cause a chemical reaction.
• a catalyst does not affect the quantity of substances produced druing the reaction.

Question 10

2

Effect of a catalyst

Answer 10

• there are three mechanisms which help explain how catalysts work:
• 1. Adsorption
• adsorption is the accumulation of molecules or atoms of a substance on the surface of another substance.
• certain particles of reactant accumulate on the surface of the catalyst, increasing the concentration of the reactants locally in that region. Thus, it is easier for the other particles of reactant to react with them.

Question 11

3

Effect of a catalyst

Answer 11

• 2. intermediate products
• intermediate products are unstable compounds or ions formed by catalysts with certain reactants, which alter decompose to form the final products of the reaction.
• When the final product is formed the catalyst returns to its intital state, allowing it to begin the process all over again.