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enthalpy of formation
The standards molar enthalpy of formation is the enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions, all reactants and products in their standard states
Enthalpy of combustion
the enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all the substances in standard states
enthalpy of atomisation
enthalpy change when one mole of gaseous atoms is produced from elements in its standard state.
lattice enthalpy of formation
Enthalpy change when on emole of a solid ionic compound is formed from its constituent ions in the gaseous state
lattice enthalpy of dissociation
enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase
enthalpy of neutralisation
enthalpy change when 1 mole of water is formed in a reaction between an acid and alkali under standard conditions
why do combustion reactions occur and why do they give out energy?
why is thermodynamics important?
it is important to understand the stability of compounds and why chemical reactions occur
first ionisation enthalpy
enthalpy change when each atom in one mole of gaseous atoms lose one electron to form one mole of gaseous 1+ ions.
first electron affinity
enthalpy change when each atom in one mole of gaseous atoms gains one election to form one mole of gaseous 1- ions
enthalpy of atomisation
enthalpy change when one mole of gaseous atoms is produced from an element in its standard state
hydration enthalpy
enthalpy change when one mole of gaseous ions become hydrated (Dissolved in water)
enthalpy of solution
enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other.
bond dissociation enthalpy
enthalpy change when one mole of covalent bonds is broken in the gaseous state
Enthalpy of vaporisation
enthalpy change when one mole of a liquid is turned into a gas
enthalpy of fusion
enthalpy change when one mole of a solid is turned into a liquid
What is a born harbour cycle?
it is a special kind type of Hess Cycle that represent the formation of an ionic compound from its elements in a series of steps.
what are the five steps in the born haber cycles
step 1 - atomisation of the metal reactant
step 2 - atomisation of the non metal reactant
step 3 - ionisation of metal
step 4 - electron affinity of the non metal
step 5 - formation of the ionic lattice
exothermic enthalpies
enthalpy of formation
enthalpy of electron affinity
lattice formation enthalpy
endothermic enthalpies
enthalpy of atomisation
enthalpy of electron affinity
ionisation enthalpy
What two factors increase the attraction and therefore the lattice formation enthalpy
higher charge of anion, smaller sizer of anion
which has a higher lattice enthalpy and why, NaBr or NaCl? (3 marks)
Cl- is smaller that Br-
Higher charge density
More strongly attracted to Na
what are the assumptions of the perfect ionic model?
Ions are point charges, their charge is distributed evenly
perfectly spherical
100% ionic bonding
no electron cloud distortion
what happens when i introduce a large anion to a small, highly charged cation?
attraction to valence electrons, valence electrons move further away from the nucleus
cloud distortion
called polarisation
what is covalent character?
when valence electrons from anion mover further away from nucleus and are drawn to the nucleus of the cation
overlap between oppositely charged ions, this is an ionic bond with covalent character
theoretical values
formation enthalpy of ionic compounds, calculated using born harbor cycle based on the perfect ionic model
experimental values
normally higher that theoretical values
this suggests that the compounds are not completely ionic.
what does the term polarisable mean
it is when the anion is large so that the outer electrons have a weaker electrostatic attraction with the nucleus and therefore the nucleus in the cation is able to attract those outer electrons, this means the anion is polarisable
what is entropy?
A measure of disorder/randomness, it is given the symbol S: J K^-1mol^-1
describe a substance with low entropy
Ordered, and regular arrangement of particles
Describe a substance with high entropy
Disorder, random arrangement of particles
states of matter in order of low to high entropy
Solid < Liquid < Gas
How calculate Entropy change
Total entropy of products - total entropy of reactants
Entropy change in surroundings
S = entropy change in the system + entropy change in the surrounding
How does an exothermic reaction increase the entropy in surroundings
Heat is released from the system into the surroundings, this increases the random motion of the particles in the surroundings, which increases the entropy
How does an endothermic reaction decrease the entropy in the surroundings
Heat is absorbed by the system from the surrounding, this decreases the motion of particles in the surroundings, decreasing the entropy
what does the entropy change in the surroundings depend on
enthalpy change of the system and temperature of surroundings
= -enthalpy change of the system/ temperature of the surroundings
what is Gibbs Free energy?
The way of predicting whether or not a chemical reaction will take place when looking at the thermodynamics of a reaction and whether it is feasible
