Thermodynamics Year 2 Flashcards
(22 cards)
What’s the H of formation?
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
What’s h of combustion
The enthalpy change when one mole of substance is completely burnt in oxygen
What’s the H of atomisation
The enthalpy change when one mole of gaseous atoms are formed from the element in its standard state under standard conditions
What’s first ionisation energy?
Standard enthalpy change when one mole of gaseous atoms is converted to a mole of gaseous +1 ions
What’s the H of electron affinity?
Standard enthalpy change when a mole of gaseous atoms is converted into a mole of gaseous -1 ions
What’s the second electron affinity?
The enthalpy change when a mole of electrons is added to a mole of gaseous -1 ions to form -2 ions
What’s the H of lattice formation
Standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions
What’s lattice dissociation H
Standard enthalpy change when one mole of solid ionic compound dissociates into its gaseous ions
What’s the H of hydration
Standard enthalpy change when one mole of gaseous ions are converted into aqueous ions or an aqueous solution
What’s the H of solution
Standard enthalpy change when one mole of solute dissolves completely in sufficient solvent to form a solution in which ions or molecules are far enough apart to not react together
What’s the mean bond enthalpy?
Enthalpy change when one mole of gaseous molecules each breaks a covalent bond to form two free radicals, averaged over a range of compounds
What’s ionic bonding
Electrons are transferred from metal atoms to non metal atoms
+ve metal ions form and -ve non metal ions form
They both have stable outer shells of electrons
These ions arrange into a lattice so that ions of opposite charge are next to each othee
What’s a born haber cycle?
A thermochemical cycle that includes all the enthalpy changes involved in the formation of an ionic compound
What must you include to help with born haber calculations?
Moles
States
What is an arrow down representing in a born haber cycle
An exothermic energy change (-ve)
What’s an arrow up representing in a born haber cycle?
Endothermic energy change (+ve)
What do larger ions lead to?
Smaller lattice enthalpies bc the opposite charges dont approach each other as closely as
How can ionic solids dissolve well?
In polar solvents
How do ionic compounds dissolve?
The lattice must be broken up- the lattice dissociation enthalpy has to be put in
The separate ions are then solvated by the solvent molecules- usually water.
These cluster round the ions so that the positive ions are surrounded by the negative end of the dipole of the water molecules and vis versa=
Cations are hydrated- enthalpy of hydration is given out
Anions are hydrated- enthalpy of hydration is given out
What is dissolving called when the solvent is water?
Hydration
What’s the trend for enthalpy change of hydration
It’s more negative for more highly charged ions and less negative for larger ions
Same trend as lattice enthalpy
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