Note:

IGCSE Chemistry Notes on Chemical Reactions for  2026-2027-2028-Exams

Syllabus Content:

6.1 Physical and chemical changes

Core 

1. Identify physical and chemical changes, and describe the differences between them

Supplement 

6.2 Rate of reaction

Core 

1. Describe the effect on the rate of reaction of: (a) changing the concentration of solutions (b) changing the pressure of gases (c) changing the surface area of solids (d) changing the temperature (e) adding or removing a catalyst, including enzymes
2. State that a catalyst increases the rate of a reaction and is unchanged at the end of a reaction 
3. Describe practical methods for investigating the rate of a reaction including change in mass of a reactant or a product and the formation of a gas 
4. Interpret data, including graphs, from rate of reaction experiments

Supplement 

1. Describe collision theory in terms of: (a) number of particles per unit volume (b) frequency of collisions between particles (c) kinetic energy of particles (d) activation energy, Ea 
2. Describe and explain the effect on the rate of reaction of: (a) changing the concentration of solutions (b) changing the pressure of gases (c) changing the surface area of solids (d) changing the temperature (e) adding or removing a catalyst, including enzymes using collision theory 
3. State that a catalyst decreases the activation energy, Ea, of a reaction 
4. Evaluate practical methods for investigating the rate of a reaction including change in mass of a reactant or a product and the formation of a gas

6.3 Reversible reactions and equilibrium

Core 

1. State that some chemical reactions are reversible as shown by the symbol ⇌
2. Describe how changing the conditions can change the direction of a reversible reaction for: (a) the effect of heat on hydrated compounds (b) the addition of water to anhydrous compounds limited to copper(II) sulfate and cobalt(II) chloride Supplement 
3. State that a reversible reaction in a closed system is at equilibrium when: (a) the rate of the forward reaction is equal to the rate of the reverse reaction (b) the concentrations of reactants and products are no longer changing
4. Predict and explain, for a reversible reaction, how the position of equilibrium is affected by: (a) changing temperature (b) changing pressure (c) changing concentration (d) using a catalyst using information provided 
5. State the symbol equation for the production of ammonia in the Haber process, N2(g) + 3H2(g) ⇌ 2NH3(g) 
6. State the sources of the hydrogen (methane) and nitrogen (air) in the Haber process 
7. State the typical conditions in the Haber process as 450°C, 20000kPa/200atm and an iron catalyst 8 State the symbol equation for the conversion of sulfur dioxide to sulfur trioxide in the Contact process, 2SO2(g) + O2(g) ⇌ 2SO3(g) 
8. State the sources of the sulfur dioxide (burning sulfur or roasting sulfide ores) and oxygen (air) in the Contact process
9. State the typical conditions for the conversion of sulfur dioxide to sulfur trioxide in the Contact process as 450°C, 200kPa/2atm and a vanadium(V) oxide catalyst 
10. Explain, in terms of rate of reaction and position of equilibrium, why the typical conditions stated are used in the Haber process and in the Contact process, including safety considerations and economics

6.4 Redox

Core 

1. Use a Roman numeral to indicate the oxidation number of an element in a compound 
2. Define redox reactions as involving simultaneous oxidation and reduction
3. Define oxidation as gain of oxygen and reduction as loss of oxygen 
4. Identify redox reactions as reactions involving gain and loss of oxygen 
5. Identify oxidation and reduction in redox reactions Supplement 
6. Define oxidation in terms of: (a) loss of electrons (b) an increase in oxidation number 
7. Define reduction in terms of: (a) gain of electrons (b) a decrease in oxidation number 
8. Identify redox reactions as reactions involving gain and loss of electrons 
9. Identify redox reactions by changes in oxidation number using: (a) the oxidation number of elements in their uncombined state is zero (b) the oxidation number of a monatomic ion is the same as the charge on the ion (c) the sum of the oxidation numbers in a compound is zero (d) the sum of the oxidation numbers in an ion is equal to the charge on the ion 
10. Identify redox reactions by the colour changes involved when using acidified aqueous potassium manganate(VII) or aqueous potassium iodide 
11. Define an oxidising agent as a substance that oxidises another substance and is itself reduced 
12. Define a reducing agent as a substance that reduces another substance and is itself oxidised 
13. Identify oxidising agents and reducing agents in redox reactions

Happy Learning,

Team,

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