EJC C5 2023 Chemical Energetics Lecture Notes (Student's copy)

2023 JC1 H2 CHEMISTRY (9729) CORE IDEA 3 - TRANSFORMATION Topic 5: CHEMICAL ENERGETICS - THERMOCHEMISTRY & THERMODYNAMICS Name: ___________________________________________ Civics Group: _________ Students 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 (H negative) or endothermic (H positive) (b) construct and interpret an energy profile diagram, in terms of the enthalpy change of the reaction and of the activation energy (c) explain and use the terms: (i) enthalpy change of reaction and standard conditions, with particular reference to: formation; combustion; hydration; solution; neutralisation; atomisation (ii) bond energy (H positive, i.e. bond breaking) (iii) lattice energy (H negative, i.e. gaseous ions to solid lattice) (d) calculate enthalpy changes from appropriate experimental results, including the use of the relationship: heat change = −mcT (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 (g) explain and use the term entropy (h) discuss the effects on the entropy of a chemical system by the following: (i) change in temperature (ii) change in phase (iii) change in the number of particles (especially for gaseous systems) (iv) mixing of particles [quantitative treatment is not required] (i) predict whether the entropy change for a given process or reaction is positive or negative (j) state and use the equation involving standard Gibbs free energy change of reaction, G : G H= TS− [the calculation of standard entropy change, S , for a reaction using standard entropies, S , is not required] (k) state whether a reaction or process will be spontaneous by using the sign of G (l) understand the limitations in the use of G to predict the spontaneity of a reaction (m) predict the effect of temperature change on the spontaneity of a reaction, given standard enthalpy and entropy changes

C h e m i c a l E n e r g e t i c s : T h e r m o c h e m i s t r y & T h e r m o d y n a m i c s E u n o i a J u n i o r C o l l e g e 2 | P a g e LECTURE CONTENT 1 Introduction ................................ ................................ ................................ .............................. 3 1.1 Enthalpy and enthalpy change