Chapter 13 Flashcards
What is lattice energy a measure of?
Ionic bond strength
What is the definition of standard lattice energy?
Standard lattice energy is the energy change when 1 mole of an ionic solid is formed from its gaseous ions under standard conditions
What is the equation for the standard lattice energy of sodium chloride?
Na+(g) + Cl-(g) —> NaCl(s)
What are standard conditions?
298K and 100kPa
What does the more negative the lattice energy mean?
The stronger the bonding
What 2 factors affect lattice energy?
Ionic charge and size
What does the higher the charge on the ions mean about the energy releases when an ionic lattice forms?
The higher the charge on the ion, the more energy released when an ionic lattice forms, due to the stronger electrostatic forces between the ions
Are lattice energies for compounds with 2+ or 2-ions or compounds with 1+ or 1- ions more exthermic?
Compounds with 2+ or 2- are more exothermic
Why does MgCl2 have a higher lattice energy (more negative) than NaCl?
Magnesium has a greater charge than sodium
Why does MgS have a higher lattice energy than MgCl2?
Because both Mg and S have double charges
How does ionic radius affect the size of the lattice energy?
The smaller the ionic radius of the ions involved, the more exothermic (the more negative) the lattice energy is
Why do ions with smaller ionic radius have larger lattice energy values?
Smaller ions have higher charge density and their smaller ions can pack more closely together
What does Hess’s law say?
The total enthalpy change of a reaction is always the same, no matter the route taken
What is Hess’s law also known as?
The conservation of energy
As you can’t calculate lattice energy directly, what do you have to use in order to calculate it?
A born-Haber cycle
What can a Born-Haber cycle be used to calculate?
Lattice energies
What does a Born-Haber cycle start with on the LHS?
The enthalpy of formation
What is the enthalpy of formation?
The change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states.
What direction does the arrow for the enthalpy of formation face in a Born-Haber cycle?
Downward
After the enthalpy of formation, what comes next in a Born-Haber cycle?
The enthalpy changes of atomisation and ionisation
In a Born-Haber cycle, what direction do the enthalpy changes of atomisation and ionisation face?
Upwards
What is the definition of the enthalpy change of atomisation?
The enthalpy change of atomisation is the enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state
What is the equation for the atomisation of sodium?
Na(s) —>Na(g)
What is the equation for the atomisation of chlorine?
1/2 Cl2(g) —> Cl(g)