Chapter 22 Flashcards
Define Lattice Enthalpy
Lattice enthalpy is the enthalpy change when one mole of ionic compound is formed from its gaseous ions under standard conditions.
What is the sign of lattice enthalpy ? Why?
Negative, as bond are forming. So its an exothermic reaction.
Why are Born-Haber Cycles used?
Used because lattice enthalpy cannot be measure directly.
Is Lattice formation endothermic or exothermic?
Endothermic
Is the formation of gaseous atoms endothermic or exothermic?
Exothermic
Is the Enthalpy change of formation endothermic or exothermic?
Exothermic
Define Enthalpy Change of Atomisation
The enthalpy change for the formation of one mole of gaseous atoms of an elements in its standard state under standard conditions.
Is Enthalpy change of atomisation exo or endothermic?
Endothermic
Define First ionisation energy
The enthalpy change when one electron is removed from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
Why is the First ionisation energy always endothermic?
Energy is required to overcome the attraction between positive nucleus and negative electron.
Define the first electron affinity
The enthalpy change when on electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
Why is the first electron affinity exothermic?
Exothermic as electron is being added is attracted to the nucleus.
What is the exception to the first electron affinity rule?
When more than one electron is added to an atom, the second on is repelled by the first, so the second electron affinity is likely to be positive.
What happens when a substance dissolves in solution?
H20 can overcome the electrostatic attractions between oppositely charged ions and break up the giant ionic lattice structure.
Define enthalpy change of solution
The enthalpy change when one mole of solute dissolves in a solvent
Define enthalpy change of hydration
The enthalpy change when one mole of gaseous ions dissolve in water to form one mole of aqueous ions
What factors effect lattice enthalpy?
- Size of ion
2. Charge on ion
How does the size of the ion effect lattice enthalpy?
- Ionic radius increases
- Attraction between ions decreases
- Lattice enthalpy is less negative
- Melting point decreases
How does the charge on the ion effect lattice enthalpy?
- Ionic charge increases
- Attraction between ions increases
- Lattice energy becomes more negative
- Melting point increases
How does size of ion affect hydration enthalpy?
- Ionic radius increases
- Attraction between ion and water molecules decreases
- Hydration energy less negative
How does the charge on an ion affect hydration enthalpy?
- Ionic charge increases
- Attraction with eater molecules increases
- Hydration energy becomes more negative
When can solubility occur?
When the energy released from hydrating the ions is equal to or greater than the energy required to break up the lattice.
Define entropy
A measure of the dispersal of energy in a system
What is symbol of entropy?
S
