2023 NJC Energetics I Lecture Notes (Students) updated 9 April

National Junior College SH 1 H2 Chemistry 1 Content ● Enthalpy changes (Δ H): ΔH of formation; combustion; hydration; solution; neutralisation; atomisation; bond energy; lattice energy; electron affinity ● Hess’ Law, including Born−Haber cycles Learning Outcomes: Candidates should be able to (a) explain that most chemical reactions are accompanied by energy changes, principally in the form of heat usually associated with the breaking and forming of chemical bonds; the reaction can be exothermic (ΔH negative) or endothermic (ΔH positive) (b) construct and interpret an energy profile diagram, in terms of the enthalpy change of the reaction and of the activation energy (see also “Reaction Kinetics” notes) (c) explain and use the terms: (i) enthalpy change of reaction and standard conditions, wi th particular reference to: formation; combustion; hydration; solution; neutralisation; atomisation (ii) bond energy (ΔH positive, i.e. bond breaking) (see also “Chemical Bonding” notes) (iii) lattice energy (ΔH negative, i.e. gaseous ions to solid lattice) (d) calculate enthalpy changes from appropriate experimental results, including the use of the relationship: heat change = mcΔT (e) explain, in qualitative terms, the effect of ionic charge and of ionic radius on the numerical magnitude of a lattice energy (f) apply Hess’ Law to construct simple energy cycles, e.g. Born -Haber cycle, and carry out calculations involving such cycles and relevant energy terms (including ionisation energy and electron affinity), with particular reference to: (i) determining enthalpy changes that cannot be found by direct experiment, e.g. an enthalpy change of formation from enthalpy changes of combustion (ii) the formation of a simple ionic solid and of its aqueous solution (iii) average bond energies Chemical Energetics All Rights Reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any other information storage and retrieval system, without prior permission in writing from the copyright owner. Copyright © 2023 National Junior College

National Junior College SH 1 H2 Chemistry 2 Note: It is not possible to measure the absolute enthalpy of the reactant or product in a system directly. We can only measure changes in enthalpy of the system when it undergoes chemical or physical changes. 1 Introduction Success Criteria: • Explain that most chemical reactions and physical processes are accompanied by changes in heat energy which is a result of the breaking and