Energy Cycles
Mission Objectives:
1. Construction of Born-Haber Cycle for group 1 & group 2 oxides and chlorides.
2. Construction of energy cycles from hydration, lattice and solution enthalpy.
3. Calculation of enthalpy changes from Born-Haber or dissolution of energy cycles.
4. Relate size and charge of ions to lattice and hydration enthalpies.
Links: TutorVista
The Born-Haber Cycle is an energy cycle for the formation of an ionic compound. It is an application of Hess' Law that combines the enthalpy change with several steps in the formation of an ionic compound.
1. Construction of Born-Haber Cycle for group 1 & group 2 oxides and chlorides.
2. Construction of energy cycles from hydration, lattice and solution enthalpy.
3. Calculation of enthalpy changes from Born-Haber or dissolution of energy cycles.
4. Relate size and charge of ions to lattice and hydration enthalpies.
Links: TutorVista
The Born-Haber Cycle is an energy cycle for the formation of an ionic compound. It is an application of Hess' Law that combines the enthalpy change with several steps in the formation of an ionic compound.
Below is a simple example of the concept. You'll want to take notes as we work through the example in class.
There are some different enthalpies that you need to be familiar with.
1. Lattice Enthalpy is the standard enthalpy change (SEC) that occurs on the formation of one mole of gaseous ions from the solid matter. Look at the example on page 358 in your text. The process is endothermic and data values are in the Data Booklet.
2. Enthalpy of Atomization. This is the SEC that occurs on the formation of one mole of separate gaseous atoms of an element in its standard state. "M" sublimates and "X" has an atom removed. Look at the example on page 358 in your text.
3. Ionization Energy. This is the SEC that occurs on the removal of one mole of electrons from one mole of atoms or cations in the gaseous phase. Metals will have multiple IEs depending on number of electrons removed. Look at the example on page 359.
4. Electron Affinity. The SEC on the ADDITION of one mole of electrons to one mole of atoms in the gaseous phase. See page 359.
These are combined to construct a Born-Haber Cycle and find either heat of formation or lattice energy of an ionic compound. To do this, add up the correct values for enthalpy changes. Keep your Data Booklet handy.
The IB requires that you know the B-H Cycle for sodium chloride, magnesium fluoride, and magnesium oxide. Examine the worked examples on page 360.
1. Lattice Enthalpy is the standard enthalpy change (SEC) that occurs on the formation of one mole of gaseous ions from the solid matter. Look at the example on page 358 in your text. The process is endothermic and data values are in the Data Booklet.
2. Enthalpy of Atomization. This is the SEC that occurs on the formation of one mole of separate gaseous atoms of an element in its standard state. "M" sublimates and "X" has an atom removed. Look at the example on page 358 in your text.
3. Ionization Energy. This is the SEC that occurs on the removal of one mole of electrons from one mole of atoms or cations in the gaseous phase. Metals will have multiple IEs depending on number of electrons removed. Look at the example on page 359.
4. Electron Affinity. The SEC on the ADDITION of one mole of electrons to one mole of atoms in the gaseous phase. See page 359.
These are combined to construct a Born-Haber Cycle and find either heat of formation or lattice energy of an ionic compound. To do this, add up the correct values for enthalpy changes. Keep your Data Booklet handy.
The IB requires that you know the B-H Cycle for sodium chloride, magnesium fluoride, and magnesium oxide. Examine the worked examples on page 360.
Enthalpy changes in solution look at the relationship between enthalpy change of solution, hydration enthalpy, and lattice enthalpy.
The SEC of solution is a change in enthalpy when one mole of a substance is dissolved in an excess of a pure solvent. The enthalpy change of hydration is the enthalpy change when one mole of gaseous ions are added to water to form a dilute solution.
Terms to know: solvation (solvents used other than water), hydration (water as the solvent), and dissolution (homogeneous phase after solute has been added).
The SEC of solution is a change in enthalpy when one mole of a substance is dissolved in an excess of a pure solvent. The enthalpy change of hydration is the enthalpy change when one mole of gaseous ions are added to water to form a dilute solution.
Terms to know: solvation (solvents used other than water), hydration (water as the solvent), and dissolution (homogeneous phase after solute has been added).
Entropy & Spontaneity
Mission Objectives:
1. Predict whether a change will result in an increase or decrease in entropy by considering the states of the reactants and the products.
2. Calculate entropy changes from standard entropy values.
3. Application of Gibbs' Free Energy equation in predicting spontaneity and calculations of various conditions of enthalpy and temperature that will affect this.
4. Relate G to position of equilibrium.
A reaction is said to be spontaneous when it moves towards completion or equilibrium under a set of conditions without external intervention. Spontaneous reactions can be endothermic or exothermic. Reactions that do not take place under a given set of conditions are said to be non spontaneous.
Recall the laws of thermodynamics. The second law focuses on entropy, which is a measure of the distribution of total available energy between particles. The greater the shift from localized to widespread, the lower the chance of the particles returning to their original state and the higher the entropy of the system.
Watch the below videos. Make sure you take notes, especially when he shows the different flowcharts showing how these terms relate to one another.
1. Predict whether a change will result in an increase or decrease in entropy by considering the states of the reactants and the products.
2. Calculate entropy changes from standard entropy values.
3. Application of Gibbs' Free Energy equation in predicting spontaneity and calculations of various conditions of enthalpy and temperature that will affect this.
4. Relate G to position of equilibrium.
A reaction is said to be spontaneous when it moves towards completion or equilibrium under a set of conditions without external intervention. Spontaneous reactions can be endothermic or exothermic. Reactions that do not take place under a given set of conditions are said to be non spontaneous.
Recall the laws of thermodynamics. The second law focuses on entropy, which is a measure of the distribution of total available energy between particles. The greater the shift from localized to widespread, the lower the chance of the particles returning to their original state and the higher the entropy of the system.
Watch the below videos. Make sure you take notes, especially when he shows the different flowcharts showing how these terms relate to one another.
Entropy is represented by delta S. It can be calculated from thermodynamic data from the Data Booklet. The standard values relate to standard conditions of temperature and pressure.
Delta S (rxn) = Delta S (products) - Delta S (reactants) (page 367)
When completing entropy calculations, remember that values are specific for different states of matter. Also recall that the coefficients used to balance the equation must be applied to molar entropy values when calculating overall entropy change.
Be sure to examine the chemical reaction and predict whether you expect the reaction to have a positive or negative entropy change based on the degree of disorder in the products and reactants.
Gibbs' Free Energy is a state function, along with entropy, temperature and enthalpy. The below video goes into detail in the relationship between entropy, enthalpy and Gibbs' Free Energy.
Delta S (rxn) = Delta S (products) - Delta S (reactants) (page 367)
When completing entropy calculations, remember that values are specific for different states of matter. Also recall that the coefficients used to balance the equation must be applied to molar entropy values when calculating overall entropy change.
Be sure to examine the chemical reaction and predict whether you expect the reaction to have a positive or negative entropy change based on the degree of disorder in the products and reactants.
Gibbs' Free Energy is a state function, along with entropy, temperature and enthalpy. The below video goes into detail in the relationship between entropy, enthalpy and Gibbs' Free Energy.
The Gibbs' Free Energy provides an effective way of focusing on a reaction system at constant temperature and pressure to determine its spontaneity. For a reaction to be spontaneous, the GFE must have a negative value. Examine Table 3 on page 369.