Collision Theory and Reaction Rate

Collision Theory

• every reaction involves the re-arrangement of atoms or ions a formation of new bonds

  • this re-arrangement requires collisions between reactant particles

  • a successful collision occurs when particles collide with both:

  • → the right orientation

  → enough energy or speed to break their bonds

  • if both conditions aven't met then the particles will just sance other without reacting

Reaction Rate

• the speed at which the chemical reaction progresses towards completion

• we need to be able to influence the reaction rate (slower for safety, faster for time)

Factors that affect chemical reactions: Temperature

• usually, increasing temperature will cause the reaction to go faster

• this is due to giving the particles more kinetic energy, which results in them moving and colliding faster, which makes exchanging elections happen quicker (more interactions)

• opposite when decreasing temperature (slower particles, less interactions)

Factors that affect chemical reactions: Concentration

• How much of the stuff you use

• More chemicals means more collisions (interactions), thus a faster reaction Ca concentrated solution will contain more dissolved porticles than a dilute solutton)

opposite is true, less chemicals, less colisions, slower reaction

• as the reaction progresses the concentration of reactants decreases

• this reduces tha frequency o collisions between particles and so the reaction slows down

Factors that speed up chemical reaction: Surface Area

• The opposite is true, less surface area, less interactions, dower reactions

• if you increase the surface area of a reactant, we increase the rate of reaction

e. g. a large marble chip is placed into acid and only the outer surface can react (there are I3 particles on the outer surface)

by having smaller pieces of the same marble chip, the surface area

increases to 21

• the area exposed for the reaction is greater so it happens taster

Factors that speed up chemical reaction: Activation Energy

• the invisible “energy barrier” that reactant molecules most overcome to break existing chemical bonds and transform into products

• minimum amount of energy required to start a chemical or physical process

Activation Energy: Catalyst

• provides an alternative reaction pathway that lowers the activation energy required for the reaction to occur

• The catalyst is not permanently changed or used up during the reaction, allowing it to be recycled and used repeatedly

• lowers the activation energy, making reactions happen faster

Activation Energy: Inhibitor

• reduces the rate of reaction by binding to specific parts of a molecule, altering its structure

• occupies reactive sites so that the actual reactants cannot engage

• interfering with catalysts (such as enzymes) or blocking direct contact between reactant molecules

• increases activation energy, making reaction happen slower