Thermodynamics Flashcards
What is enthalpy of formation
The enthalpy change when one mole of a compound is formed from its elements, with all reactants and products in their standard states under standard conditions
Is enthalpy of formation exo or endothermic
It is exothermic
What is enthalpy of atomisation
Enthalpy change for the formation of one mole of gaseous atoms from elements in their standard state
What is the equation for enthalpy of atomisation of Na (state what type of bond is broken)
Na(s) —> Na(g)
( metallic bonds broken
What is the enthalpy of atomisation equation for Cl (state what type of bond is broken)
1/2Cl2(g) —> Cl(g)
Intermolecular forces broken
What is first ionisation energy
X(g) —> X+ + e-
Is ionisation energy an exothermic or endothermic reaction
It is endothermic
Why is ionisation energy endothermic
Because energy is required to overcome the electrostatic force of attraction between the nucleus of the atom and the electron being removed
Explain why successive ionisation energies are more endothermic
It is harder to remove an electron from a more positive ion
Electron that is being removed is closer to the nucleus therefore more strongly attracted
What is the equation for 1st elctron affinity
X(g) + e- –> X-(g)
Is 1st electron affinity exo or endothermic
Exothermic
Explain why 1st electron affinity has a negative ΔH
There is a net attractive force between the nucleus of the atom and the electron added therefore energy is released
What is the equation for second electron affinity
X-(g) + e- –> X2-(g)
Explain why second electron affinity and and successive energy affinities are endothermic
Repulsion between the negative ion and electron
Therefore energy is required to overcome repulsion
State a trend in successive electron affinities
They get progressively more endothermic
What is Lattice dissociation
The standard enthalpy change for the dissociation of one mole of a solid ionic lattice into its gaseous ions
What is the general formula for lattice dissociation
MX(s) —> M+(g) + X-(g)
What is the symbol for lattice dissociation
ΔHL
What is the symbol for electron affinity
ΔHea
What is the symbol for ionisation energy
ΔHi
What is the symbol for enthalpy of atomisation
ΔHat
What is the symbol for enthalpy of formation
ΔHf
What is enthalpy of solution
Enthalpy change for: MX(s) —-> M+ (aq) + X-(aq)
What is enthalpy of hydration
Enthalpy change for X+/-(g) ——> X+/-(aq)
Draw a solution Hess cycle for Nacl
-
What is in the top left of a solution Hess cycle
Compound in solid state
What is at the bottom of a solution Hess cycle
Ions in gaseous state
What is in the top right of a solution Hess cycle
Ions in aqueous state
What does the arrow going from the compound to gaseous ions represent in a solution Hess cycle
Enthalpy of lattice dissociation
What do the arrows going from gaseous ions to aqueous ions represent in a solution Hess cycle
Enthalpy of Hydration
What does the arrow going from the solid ionic compound to aqueous ions represent in a solution Hess cycle
Enthalpy of solution
What does the arrow going from the solid ionic compound to aqueous ions represent in a sol
What is the equation for enthalpy of solution
Enthalpy of lattice dissociation + Enthalpy of hydration positive ion + enthalpy of hydration of negative ion
What affects the value of enthalpy of lattice formation/dissociation
Smaller & highly charged ions have a higher charge density - giving stronger electrostatic force of attraction between oppositely charged ions
Gives more exo value for formation
Gives more enforcing value for dissociation
What affects the value of enthalpy of hydration for positive ions
The force of attraction between the delta negative O of water, and the positive ion
What causes a stronger force of attraction between a delta negative oxygen on a water molecule and a positive ion (how does it affect the value of enthalpy of hydration)
Smaller more positive ions will have a higher charge density
Will attract delta H oxygen on H2O stronger
Which gives a more exothermic value for enthalpy of hydration
What affects the value of enthalpy of hydration for negative ions
The attraction between the delta positive H on a H2O molecule and the negative ion
What affects the attraction between delta positive H on a water molecule and a negative ion (how does it affect the value of enthalpy of hydration)
Smaller more negative ions will have a larger charge density
This will attract the delta positive H on the H2O stronger
This gives a more exothermic value for enthalpy of hydration
When is covalent character more prevalent
The more charge dense the positive ion is, as well as when there is a larger or more negative, negative ion.
(n+ more polarising, n- more polarisable)
When does the most covalent character occur
When we have small, highly positive ions are bonded to highly negative ions
What does the perfect ionic model assume
Assumes that the ions are perfect spheres (no covalent character)
When will the born barber value for enthalpy of lattice F/D be similar to the value from the PIM equation
When there is no/little covalent character
If there is covalent character present, how will the born haber value differ from the P.I.M value for lattice enthalpy of F/D
The value will typically be larger
Either more -ve for lattice enthalpy of dissociation
Or more +ve for lattice enthalpy of formation
What is bond enthalpy
The amount of energy required to break one mole of a specific covalent bond in the gas phase
