Chemistry 0620 Topic 5 Notes - Chemical Energetics
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Course
Cambridge IGCSE Chemistry
Institution
Fourth Year / 10th Grade
These topic notes have been made in conjunction with the 0620 Cambridge IGCSE Chemistry syllabus, utilising diagrams and explanations from various study resources. They cover all the syllabus statements for Topic 5 of the syllabus - Chemical Energetics. The notes are written in concise bullet point...
5.1 EXOTHERMIC AND ENDOTHERMIC REACTIONS---------------
● Exothermic reaction: transfers thermal energy (heat) to the surroundings leading to an increase in the
temperature of the surroundings
○ BOND MAKING (energy released when atoms join to form stable compounds - products)
● Endothermic reaction: takes in thermal energy from the surroundings leading to a decrease in the
temperature of the surroundings - BOND BREAKING (energy used to break all bonds of reacting
compounds - reactants)
○ Bond energy (kJ/mol): energy needed to break bonds / energy released when the same bonds
form
● Activation energy (Ea): the minimum energy that colliding particles must have to react
● Enthalpy Change (ΔH): transfer of thermal energy during a reaction
○ Enthalpy change = energy used to break bonds of reactants - energy released when products
formed
○ ENDO: ΔH = +ve → Energy used to break bonds of reactants > energy released when products
formed
○ EXO: ΔH = -ve → Energy used to break bonds of reactants < energy released when products
formed
REACTION PATHWAY DIAGRAMS
● Product line is lower in energy than the reactant line
because the reactants have lost energy → energy has
been transferred to the surroundings and therefore the
surroundings gain energy and become hotter
● Activation energy is Ea (between reactant line and top
of bump)
● ΔH: bc product is lower in energy than reactant,
therefore the enthalpy change is negative
● Product line is above reactant line - higher in energy
than reactant
● ΔH is positive bc the product is higher in energy than
reactant
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