Chapter 22 - Enthalpy and Entropy Flashcards
Lattice Enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions
symbol for lattice enthalpy
ΔleH
standard enthalpy change of formation
the enthalpy change that occurs when one mole of a compound is formed from its elements under standard conditions, with all products and reactants in their standard states
symbol for enthalpy change of formation
ΔfH
standard enthalpy change of atomisation
the enthalpy change that occurs in the formation of one mole of gaseous atoms from the element in its standard state, under standard conditions
symbol for enthalpy change of atomisation
ΔatH
first ionisation energy
the enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
symbol for ionisation energy
ΔieH
first electron affinity
the enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
symbol for electron affinity
ΔeaH
standard enthalpy change of solution
the enthalpy change that occurs when one mole of a solute dissolves in a solvent
symbol for enthalpy change of solution
ΔsolH
enthalpy change of hydration
the enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions
symbol for enthalpy change of hydration
ΔhydH
how does ionic size affect lattice enthalpy
DOWN A GROUP
- ionic radius increases
- attraction between ions decreases
- ΔleH becomes less negative
- melting point decreases
how does ionic charge affect lattice enthalpy
ACROSS A PERIOD
- ionic charge increases
- greater attraction between ions
- ΔleH becomes more negative
- melting point increases
how does ionic size affect enthalpy change of hydration
DOWN GROUP
- increased ionic radius
- less attraction between ions and water molecules
- ΔhydH becomes less negative
how does ionic charge affect enthalpy change of hydration
ACROSS A PERIOD
- ionic charge increases
- more attraction between ions and water molecules
- ΔhydH becomes more negative
define entropy (S)
a measure of the dispersal of energy in a system which is greater the more disordered a system is
How to calculate entropy change
ΔS = ΣΔS(products) - ΣΔS(reactants)
Gibb’s free energy equation
ΔG = ΔH − TΔS
when is a reaction feasible (spontaneous)
ΔG < 0
what are the limitations of predictions made by ΔG about feasibility
some reactions have a high activation energy leading to a slow rate at a given temperature.
ΔG doesn’t take kinetics or rate of reaction into account.
