Topic 13- Energetics II Flashcards
Define lattice energy
the energy change when one mole of an ionic
solid is formed from its gaseous ions
Define enthalpy change of atomisation
1 mole of gaseous atoms from an element in its standard state under standard conditions
Define electron affinity
the energy change when one electron is added to each atom in a one mole sample of gaseous atoms or ions.
What does the polarisability of an anion depend on?
It’s radius and it’s charge
What does the polarisability of an anion depend on?
It’s radius and its charge
What does the polarising power of a cation depend on?
Radius and charge
Define enthalpy change of solution
enthalpy change when mole of substance is dissolved in solvent under standard conditions.
Define enthalpy change of hydration
The enthalpy change when one mole of gaseous ions dissolves in water to form one mole of aqueous ions under standard conditions
What does polarisation mean?
positive charge from the cation attracts electrons towards it from the anion.
lattice energy provides a measure of ….. ….. strength
Ionic bond strength
Give the equation used to find entropy change of the system
∆S˚system =ΣS˚products - ΣS˚reactant
In an exothermic reaction energy is given out into the surroundings. The number of ways of arranging the energy therefore…… and so the entropy of surroundings …….. and is ……..
number of ways arranging the energy increases and so does the entropy of surroundings and is POSITIVE
In an endothermic reaction energy is transferred from the surroundings. The number of ways of arranging the energy in the surroundings therefore decreases and so the entropy of the surroundings ……… and is ……..
decreases and is negative
Equation for total entropy change
Entropy change total = Entropy change system + Entropy change of surroundings
What is entropy?
a measure of disorder of a system (the number of ways that particles can be arranged and the number of ways that the energy can be shared between particles
What 3 things affect entropy
physical state i.e gas = high entropy
dissolving- dissolved particles can move freely
more particles=more entropy
Substances are more energetically stable when there’s ….. disorder
Substances are more energetically stable when there is MORE DISORDER!
what are the units of entropy
J K-1 mol-1
how do you calculate the free energy change?
enthalpy change - temperature*entropy change of system
∆G = ∆H -T∆Ssystem
What’s bond enthalpy?
Average enthalpy change when breaking a mole of identical bonds in the gas phase
A reaction is more likely to happen if
The reaction increases the no.of moles of substance
exothermic
reaction produces gas and consumes solid
∆G is negative then the reaction is …
feasible
∆G is positive then the reaction is ….
not feasible
What is the natural direction of change for entropy?
Increasing in total entropy (+entropy change)
What 2 things does the theoretical lattice value assume?
ions are perfect spheres
charge is evenly distributed
Why do substances want to increase their disorder?
So that they’re more energetically stable
Why are some reactions feasible even when the energy change is endothermic?
As they are moving to try to increase their entropy (e.g. more molecules)
When would you expect an increase in entropy when looking at an equation?
If the products of the forward reactions have more disorder e.g. more gas or more moles
Why doesn’t a …… ∆G guarantee a reaction?
a negative ∆G doesn’t guarantee a reaction as the reaction may have a really high activation energy
Reactions with negative ∆G, therefore feasible, have …… values for their equilibrium constants
negative ∆G = K GREATER than 1
value LARGE IN MAGNITUDE
Reactions with positive ∆G, therefore not feasible, have …… values for their equilibrium constants
positive ∆G = K smaller than 1
value small IN MAGNITUDE
High lattice enthalpy (large exothermic value) is due to what?
strong attraction between ions of HIGH CHARGE DENSITY
Define Bond dissociation enthalpy
Energy required to break 1 mole of gaseous bonds to form gaseous atoms
