TUTTEE ACADEMY LOGO
broken image
  • Home
  • About Us
  • Subjects 
    • CHEMISTRY
    • BIOLOGY
    • PHYSICS
    • MATHEMATICS
    • PSYCHOLOGY
    • ECONOMICS
    • BUSINESS
    • COMPUTER SCIENCE
    • CHINESE
    • ENGLISH
    • SPANISH
    • IBDP IA / EE
    • IBDP TOK
    • ONLINE TUTORIAL
  • Exam Boards 
    • IBDP
    • IBMYP
    • IGCSE & GCSE
    • HKDSE
    • GCE A-LEVELS
  • Courses 
    • IBDP Tuition
    • GCE A-Level Tuition
    • IBMYP Tuition
    • I/GCSE Tuition
    • HKDSE Tuition
  • Admission Test Prep 
    • PREDICTED GRADE
    • SAT / SSAT
    • UKISET (UK)
    • BMAT
    • UKCAT / UCAT
    • LNAT
    • TMUA (Cambridge)
  • Student Results 
    • IBDP STUDENT RESULTS
    • IGCSE & GCSE MATHEMATICS
    • A-LEVEL STUDENT RESULTS
    • IGCSE STUDENT RESULTS
    • GCSE STUDENT RESULTS (UK)
    • HKDSE STUDENT RESULTS
    • OUR STORIES
  • Question Bank
  • Resources
SCHEDULE A LESSON NOW

AS/A-level Chemistry - Collision Theory 

Physical Chemistry, Collision Theory, Kinetics 

· AS Chemistry,A-level Chemistry,Physical chemistry,Kinetics,Collision Theory

Collision Theory

Reactions occur by molecules colliding. However only a small fraction of these collisions lead to a reaction. For a collision to be effective molecules must collide in the correct orientation and must have sufficient energy. The minimum energy needed is called the activation energy.

broken image

Do you remember the definitions of AS/A-level Chemistry regarding exothermic and endothermic reactions? 👨‍🏫

  • In an exothermic reaction,  reacting chemicals lose energy and give it out to the surroundings, so the products have a lower energy than the reactants.
  • In an endothermic reaction the enthalpy of the products is more than the enthalpy of the reactants and heat is taken in.

     ΔH = Eaf - Eab

Where Eaf is the activation energy of the forward reaction

Where Eab is the activation energy of the reverse reaction

For an exothermic reaction, Eaf is smaller than Eab and ΔH is negative.

For an endothermic reaction, Eaf is bigger than Eab and ΔH is positive

Effect of Concentration (pressure) on reaction rates

  • If the concentration of the reactant increases, the reaction rate increases. There are more molecules in the same volume so there is a greater chance of collision, and therefore a greater chance that there will be more collisions with energy greater than the activation energy.

  • For a solid increasing surface area has the same effect

  • In a gaseous reaction, increasing the pressure is the same as increasing the concentration.

Effect of temperature on reaction rate

If the temperature of a reaction increases, so does the rate. At higher temperatures molecules have a higher kinetic energy and are moving faster, meaning more collisions and more molecules with energy greater than the activation energy.

In AS/A-level chemistry, understanding the graph is very important as it helps your understanding, don't just memories the definitions!👩‍🏫

broken image

The areas under the two curves are equal and proportional to the total number of molecules in the sample.

  • The curves do not touch the energy axis
  • At as higher temperature, T2, the peak moves to the right (higher energy) with a lower height.
  • Only the molecules with energy equal to or greater than the activation energy, Ea, will be able to react.
  • At the higher temperature, T2, many more molecules have sufficient energy to react and so the rate increases significantly.

Catalyst 

  • A catalyst lowers the activation energy of a reaction by providing an alternative route for the reaction.
  • A catalyst increases the rate of a chemical reaction without being used up. A catalyst does take part in the reaction but is unchanged and can be recovered at the end.
broken image

At the same temperature, a greater proportion of the reactant molecules will have sufficient energy to overcome the activation energy for a catalysed reaction.

broken image

For a reversible reaction, a catalyst increases the rate of the forward and backward reactions by the same amount, therefore it does not affect the position of equilibrium, but the position of equilibrium is reached quicker.

There are two types of catalyst: heterogeneous and homogeneous.

Heterogeneous

A heterogeneous catalyst is in a different phase from the reactants, i.e. a different form (solid, liquid, gas.)

Homogeneous 

A homogeneous catalyst is in the same phase as the reactants. These catalysts take an active part in the reaction rather than being an inactive spectator.

Reference:

https://getrevising.co.uk/resources/wjec_as_chemistry_kinetics

This is the end of the topic!

broken image

CLICK HERE TO LEARN MORE ABOUT OUR A-LEVEL CHEMISTRY COURSES

SIGN UP FOR A FREE A-LEVEL CHEMISTRY TRIAL

Drafted by Cherry (Chemistry)

Subscribe
Previous
AS/A-level Chemistry - Acid Anhydrides
Next
AS/A-level Chemistry - Phenol
 Return to site
Profile picture
Cancel
Cookie Use
We use cookies to improve browsing experience, security, and data collection. By accepting, you agree to the use of cookies for advertising and analytics. You can change your cookie settings at any time. Learn More
Accept all
Settings
Decline All
Cookie Settings
Necessary Cookies
These cookies enable core functionality such as security, network management, and accessibility. These cookies can’t be switched off.
Analytics Cookies
These cookies help us better understand how visitors interact with our website and help us discover errors.
Preferences Cookies
These cookies allow the website to remember choices you've made to provide enhanced functionality and personalization.
Save