Enthalpy And Entropy Flashcards
Define lattice enthalpy
Enthalpy change when 1 mol of an ionic compound is formed from its gaseous ions under standard conditions
What is lattice enthalpy
The energy needed to form ionic bonds
Is lattice enthalpy endothermic or exothermic
Exothermic because bonds are formed
Define the standard enthalpy change of formation
Enthalpy change when 1 mol of a compound is formed from its constituent elements under standard conditions
Define standard enthalpy change of atomisation
Enthalpy change when 1 mol of gaseous atoms form from its constituent elements under standard conditions
Is the enthalpy change of atomisation endothermic or exothermic
Endothermic because bonds are broken
Define first ionisation energy
Enthalpy change when 1 electron is removed form each atom in one mol of gaseous atoms to form 1 mol of gaseous 1+ ions
Are first ionisation energies exothermic or endothermic
Endo because energy needed to overcome attraction of electron to nucleus
Define standard electron affinity
Enthalpy change when an electron is added to each atom in 1 mol of gaseous atoms to form 1 mol of gaseous 1- ions
Are standard electron affinities endothermic or exothermic
Exothermic
Energy released when electron is attracted to the nucleus
Are successive electron affinities endothermic or exothermic
Always endothermic
Energy needed to overcome repulsive force os negetive ion
How do you indirectly fing the lattice enthalpy
Using born haber cycles
Define the enthalpy change of solution
Enthalpy change when 1 mol of solute dissolves in solvent
Water overcomes ionic bonds
Define the enthalpy change of hydration
Enthalpy change when 1 mol of gaseous atoms are dissolved to form 1 mol of aqueous ions
What stages does dissolving involve
Breaking of ionic bonds to form gaseous ions
Dissolving of gaseous ions to produce aqueous ions
What does the negetive of the lattice enthalpy mean
The energy needed to break the ionic lattice
What factors affect lattice enthalpy
Ionic radius and charge
How does ionic radius affect lattice enthalpy
Smaller radius = stronger attraction between ions = more negetive enthalpy
Larger charge density
How does ionic charge affect lattice enthalpy
Larger charge = stronger attraction between ions = more negetive enthalpy
Larger charge density
Why can lattice enthalpy be used to predict melting point
More negetive lattice enthalpy stronger bonds= higher melting point
Factors affecting enthalpy of hydration
Ionic radius and charge
How does ionic radius affect enthalpy of hydration
Large radius= less attraction between ions and water
Hydration enthalpy is less negetive
How does the ionic charge affect enthalpy of hydration
Larger charge = Larger attraction between ions and water
More negetive enthalpy
How can you predict solubility
More negetive enthalpy of solution = more likely to Dissolve
Define Entropy
Increase in disorder
Order the states form least to most Entropy
Solid liquid gas
What is the value for Entropy at oK
O
What does negetive and positive Entropy change mean
Negetive = more ordered
Positive = less ordered more random
What is the sign for the Entropy change from solid to liquid
Positive
Define Entropy change
Entropy one one mole of a substance under standard conditions
How is Entropy change calculated
Entropy of products - Entropy of reactants
What must the value of Entropy change be for a reaction to be feasible
> 0
Define feasibility
Whether a reaction is energetically possible/ spontaneous
What is the value for gibbs free energy for a reaction to be feasible and just feasible
<0
=0
Why might G<0 but not spontaneous
Large Ea so slow rate of reaction
