Section 1 : Physical Chemistry
Kinetics
Collision Theory
The collision theory states that reactions can only occur when collisions take place between particles
having suf cient energy - this energy is called the activation energy.
• Activation energy (Ea): the minimum amount of energy which the reacting particles require for a
successful reaction.
- Hence most collisions do not lead to a reaction, as only a very small proportion of particles collide
w/ energy greater than the activation energy.
Main Factors which affect the Rate of Reaction
Rate of reaction: the change in conc. of a reactant or product in a given amount of time.
• Collision theory is used to explain the main factors which affect the rate of a chemical reaction…
Concentration
• If conc. of a reactant is ↑
• More particles of that reactant are present in a given volume
• Leading to more successful collisions between reactant particles in a given period of time
• This causes the rate of reaction to ↑.
Pressure
• If pressure on a gaseous reaction system is ↑
• The particles are forced closer together
• Leading to more successful collisions between reactant particles in a given period of time
• This causes the rate of reaction to ↑.
Temperature
• If temp. ↑, the particles gain more KE + move faster
• Leading to more frequent successful collisions between reactant particles in a given period of time
• This causes the rate of reaction to ↑.
Surface Area of Solid Reactants
• ↑ SA of solid reactants ↑ the exposed surface of the reactants.
• This ↑ the no. of successful collisions in a given period of time
• Which ↑ the rate of the reaction.
Presence of a Catalyst
• A catalyst ↑ the rate of reaction w/out being used up.
- Catalyst: a substance that ↑ the rate of a chemical reaction w/out being changed in chemical
composition or amount.
• A catalyst works by providing an alternative reaction pathway of lower activation energy.
• By lowering the activation energy, more collisions are successful in a given period of time + so the
rate of reaction ↑.
- Catalysts are important in many industrial processes by speeding up the process + so reducing
costs.
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Kinetics
Collision Theory
The collision theory states that reactions can only occur when collisions take place between particles
having suf cient energy - this energy is called the activation energy.
• Activation energy (Ea): the minimum amount of energy which the reacting particles require for a
successful reaction.
- Hence most collisions do not lead to a reaction, as only a very small proportion of particles collide
w/ energy greater than the activation energy.
Main Factors which affect the Rate of Reaction
Rate of reaction: the change in conc. of a reactant or product in a given amount of time.
• Collision theory is used to explain the main factors which affect the rate of a chemical reaction…
Concentration
• If conc. of a reactant is ↑
• More particles of that reactant are present in a given volume
• Leading to more successful collisions between reactant particles in a given period of time
• This causes the rate of reaction to ↑.
Pressure
• If pressure on a gaseous reaction system is ↑
• The particles are forced closer together
• Leading to more successful collisions between reactant particles in a given period of time
• This causes the rate of reaction to ↑.
Temperature
• If temp. ↑, the particles gain more KE + move faster
• Leading to more frequent successful collisions between reactant particles in a given period of time
• This causes the rate of reaction to ↑.
Surface Area of Solid Reactants
• ↑ SA of solid reactants ↑ the exposed surface of the reactants.
• This ↑ the no. of successful collisions in a given period of time
• Which ↑ the rate of the reaction.
Presence of a Catalyst
• A catalyst ↑ the rate of reaction w/out being used up.
- Catalyst: a substance that ↑ the rate of a chemical reaction w/out being changed in chemical
composition or amount.
• A catalyst works by providing an alternative reaction pathway of lower activation energy.
• By lowering the activation energy, more collisions are successful in a given period of time + so the
rate of reaction ↑.
- Catalysts are important in many industrial processes by speeding up the process + so reducing
costs.
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