• 7.1-Decomposition reactions-Set-1-qp-ms.pdf
  • 7.1-Decomposition reactions-Set-2-qp-ms.pdf
  • 7.1-Decomposition reactions-Set-3-qp-ms.pdf
  • 7.1-Decomposition reactions-Set-4-qp-ms.pdf
  • 7.2-Displacement reactions-Set-1-qp-ms.pdf
  • 7.3-Photochemical reactions-Set-1-qp-ms.pdf
  • 7.4-Physical-Chemical changes-Set-1-qp-ms.pdf
  • 7.5-ROR-Precipitate formation-Set-1-qp-ms.pdf
  • 7.6-ROR-Collecting gas-Set-1-qp-ms.pdf
  • 7.6-ROR-Collision theory-Set-1-qp-ms.pdf
  • 7.7-Factors affecting equilibrim-Set-1-qp-ms.pdf
  • 7.7-Reversible reactions-Equilibrim-Set-1-qp-ms.pdf
  • 7.7-Reversible reactions-Equilibrim-Set-2-qp-ms.pdf
  • 7.8-Redox reactions-Set-1-qp-ms.pdf

IGCSE Chemistry Revision Notes for Paper 4 Extended Theory  on  Chemical Reactions

Concepts that the exam aims to test you are are:

Syllabus Objectives:

7.1 Physical and chemical changes


  • Identify physical and chemical changes, and understand the differences between them

7.2 Rate (speed) of reaction


  • Describe and explain the effect of concentration, particle size, catalysts (including enzymes) and temperature on the rate of reactions 
  • Describe the application of the above factors to the danger of explosive combustion with fine powders (e.g. flour mills) and gases (e.g. methane in mines) 
  • Demonstrate knowledge and understanding of a practical method for investigating the rate of a reaction involving gas evolution 
  • Interpret data obtained from experiments concerned with rate of reaction Note: Candidates should be encouraged to use the term rate rather than speed.


  • Devise and evaluate a suitable method for investigating the effect of a given variable on the rate of a reaction 
  • Describe and explain the effects of temperature and concentration in terms of collisions between reacting particles. (An increase in temperature causes an increase in collision rate and more of the colliding molecules have sufficient energy (activation energy) to react whereas an increase in concentration only causes an increase in collision rate.) 
  • Describe and explain the role of light in photochemical reactions and the effect of light on the rate of these reactions. (This should be linked to section 14.4.) 
  • Describe the use of silver salts in photography as a process of reduction of silver ions to silver; and photosynthesis as the reaction between carbon dioxide and water in the presence of chlorophyll and sunlight (energy) to produce glucose and oxygen

7.3 Reversible reactions


  • Understand that some chemical reactions can be reversed by changing the reaction conditions. (Limited to the effects of heat and water on hydrated and anhydrous copper(II) sulfate and cobalt(II) chloride.) (Concept of equilibrium is not required.)


  • Predict the effect of changing the conditions (concentration, temperature and pressure) on other reversible reactions 
  • Demonstrate knowledge and understanding of the concept of equilibrium

Course content