Year 13- Thermodynamics Flashcards
Enthalpy change of formation
Enthalpy change when 1 mole of
the compound is formed from its elements under standard conditions (298K and 100kpa), all
reactants and products being in their standard states
Enthalpy of atomisation
enthalpy change when
1 mole of gaseous atoms is formed from the element in its
standard state
Enthalpy of sublimation
the enthpy change for a solid metal turning to gaseous atoms
numerically the same as the enthalpy of atomisation
Bond association energy
the standard molar enthalpy change
when one mole of a covalent bond is broken into two gaseous
atoms (or free radicals
First ionisation energy
the enthalpy change required to
remove 1 mole of electrons from 1 mole of gaseous atoms to form
1 mole of gaseous ions with a +1 charge
Second ionisation energy
the enthalpy change to
remove 1 mole of electrons from one mole of gaseous 1+ ions
to produces one mole of gaseous 2+ ions.
First electron affinity
the enthalpy change that occurs when 1
mole of gaseous atoms gain 1 mole of electrons to form 1 mole of
gaseous ions with a –1 charge
Second electron affinity
s the enthalpy change when one
mole of gaseous 1- ions gains one electron per ion to produce
gaseous 2- ions
Enthalpy of lattice formation
s the standard enthalpy change
when 1 mole of an ionic crystal lattice is formed from its
constituent ions in gaseous form.
Enthalpy of lattice dissociation
the standard enthalpy
change when 1 mole of an ionic crystal lattice form is separated
into its constituent ions in gaseous form
Enthalpy of hydration
Enthalpy change when one mole of gaseous ions become
aqueous ions
Enthalpy of solution
the standard enthalpy change
when one mole of an ionic solid dissolves in a large enough
amount of water to ensure that the dissolved ions are well
separated and do not interact with one another
What does the strength of enthalpy of lattice formation depend on?
the ion size and the ion charge
How does the ion size affect enthalpy of lattice formation?
the larger the ions, the less negative it is as the charges become further apart and have a weaker attractive force between them
How does the ion charge affect enthalpy of lattice formation?
the bigger the charge, the greater the attraction between ions so the enthalpy is stronger
Down a group, what happens to the lattice enthalpies?
it becomes less negative
What do theoretical lattice enthalpies assume?
a perfect ionic model where the ions are 100% ionic and the attractions are purely electrostatic
Why is the theoretical lattice enthalpy not accurate?
because some compounds have some covalent character- it tends towards giant covalent so the lattice is stronger than it is if 100% ionic. this make the born-Haber value larger than the theoretical value.
How does covalent character affect the difference between theoretical and experimental values?
the more the covalent character, the bigger the difference in values
What makes a negative ion polarised?
when it becomes more covalent, the charge cloud is distorted.
What is entropy?
a measure of disorder in a system
Which one has a bigger jump in entropy- boiling or melting?
boiling
What leads to a positive entropy change?
an increase in disorder
What is the unit for entropy?
J K-1 mol-1
Equation for entropy
sum of entropy of products- sum of entropy of reactant
Equation for gibbs-free energy
∆G = ∆H - T∆S
Units for gibbs-free energy
KJ mol-1
When is gibbs-free energy negative?
when there is a spontaneous change
What causes gibbs-free energy to be negative?
a reaction that has increasing entropy (positive) and is exothermic (-ve ∆H)
Effect of temp on feasability
If ∆S is -ve, increasing temp makes it more likely that ∆G is negative
What should ∆G be for a reaction to be feasible?
0 or negative
How does the straight line equation apply to gibbs-free energy equation?
y=mx + c
c= ∆H
m= -∆S
x= T
On a straight line graph, what does a positive gradient mean?
∆S is negative
Enthalpies of solution- what happens when an ionic lattice dissolves in water?
bonds in the lattice are broken and new bonds are formed between the metal ions and water molecules
Equation for enthalpy of solution
∆Hsolution =∆HL dissociation + sum of V hydH
