15. Energetics/thermochemistry
15. Energetics/thermochemistry
15.1 Energy cycles
Nature of science:
Making quantitative measurements with replicates to ensure reliability - energy cycles allow for the calculation of values that cannot be determined directly.
Understandings:
Representative equations (eg M+(g) → M+(aq)) can be used for enthalpy/energy of hydration, ionization, atomization, electron affinity, lattice, covalent bond and solution.
Enthalpy of solution, hydration enthalpy and lattice enthalpy are related in an energy cycle.
Applications and skills:
Construction of Born-Haber cycles for group 1 and 2 oxides and chlorides.
Construction of energy cycles from hydration, lattice and solution enthalpy. For example dissolution of solid NaOH or NH₄Cl in water.
Calculation of enthalpy changes from Born-Haber or dissolution energy cycles.
Relate size and charge of ions to lattice and hydration enthalpies.
Perform lab experiments which could include single replacement reactions in aqueous solutions.
15.2 Entropy and spontaneity
Nature of science:
Theories can be superseded - the idea of entropy has evolved through the years as a result of developments in statistics and probability.
Understandings:
Entropy (S) refers to the distribution of available energy among the particles. The more ways the energy can be distributed the higher the entropy.
Gibbs free energy (G) relates the energy that can be obtained from a chemical reaction to the change in enthalpy (△H), change in entropy (△S), and absolute temperature (T).
Entropy of gas>liquid>solid under same conditions.
Applications and skills:
Prediction of whether a change will result in an increase or decrease in entropy by considering the states of the reactants and products.
Calculation of entropy changes (△S) from given standard entropy values (S⁰).
Application of △G⁰=△H⁰−T△S⁰ in predicting spontaneity and calculation of various conditions of enthalpy and temperature that will affect this.
Relation of △G to position of equilibrium.
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