Essential ideas
- The concept of the energy change in a single step reaction being equivalent to the summation of smaller steps can be applied to changes involving ionic compounds.
- A reaction is spontaneous if the overall transformation leads to an increase in total entropy (system plus surroundings). The direction of spontaneous change always increases the total entropy of the universe at the expense of energy available to do useful work. This is known as the second law of thermodynamics.
15.1 Born Haber cycles (see worksheet below for definitions and practice examples).
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15.1 Born Haber cycles
Understandings: 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. Calculation of enthalpy changes from Born-Haber or dissolution energy cycles. |
15.1 The effect of ionic radius and ionic charge on the lattice enthalpies of different ionic compounds.
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15.1
Applications and skills: Relate size and charge of ions to lattice and hydration enthalpies |
15.1 Enthalpy change of solution and hydration
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Understandings:
Enthalpy of solution, hydration enthalpy and lattice enthalpy are related in an energy cycle. Applications and skills: Calculation of enthalpy changes from Born-Haber or dissolution energy cycles. Relate size and charge of ions to lattice and hydration enthalpies. |
15.1 Standard enthalpy changes of formation and combustion
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This video covers the standard enthalpy changes of formation and combustion.
Please note that the standard conditions are now 298 K and 100.0 kPa. |
15.2 Predicting entropy changes
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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. Entropy of gas>liquid>solid under same conditions. Application 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. |
15.2 Calculating entropy changes
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Application and skills:
Calculation of entropy changes (ΔS) from given standard entropy values (Sº). |
15.2 Entropy and spontaneity
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Essential idea: A reaction is spontaneous if the overall transformation leads to an increase in total entropy (system plus surroundings). The direction of spontaneous change always increases the total entropy of the universe at the expense of energy available to do useful work. This is known as the second law of thermodynamics.
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15.2 Gibbs free energy
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Application and skills:
Application of ∆G° = ∆H° − T∆S ° in predicting spontaneity and calculation of various conditions of enthalpy and temperature that will affect this. |
15.2 Calculating ∆G° using ∆G°f values
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Calculating Gibbs free energy changes using Gibbs free energy of formation values.
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15.2 Effect of ΔH, ΔS and T on the spontaneity of a reaction
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15.2 Effect of ΔH, ΔS and T on the spontaneity of a reaction
Application and skills: Application of ∆G °= ∆H° − T∆S ° in predicting spontaneity and calculation of various conditions of enthalpy and temperature that will affect this. |
15.2 /17.1 ΔG and equilibrium
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Understandings:
The position of equilibrium corresponds to a maximum value of entropy and a minimum in the value of the Gibbs free energy. The Gibbs free energy change of a reaction and the equilibrium constant can both be used to measure the position of an equilibrium reaction and are related by the equation, ∆G = −RT lnk Applications and skills: Relationship between ∆G and the equilibrium constant. Calculations using the equation ∆G = −RT lnk |