Thermochemical Definitions Flashcards
What is enthalpy change?
The heat energy change at constant pressure.
What is lattice formation enthalpy?
Enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase.
What is lattice dissociation enthalpy?
Enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase.
What is enthalpy of formation?
Enthalpy change when 1 mole of a compound is formed from its elements, with all reactants and products in their standard states.
What is first ionisation energy?
Energy required to remove one mole of electrons from one mole of atoms in the gaseous state (to form 1 mole of gaseous unipositive ions).
What is second ionisation energy?
Energy required to remove one mole of electrons from one mole of unipositive ions in the gaseous state (to form 1 mole of gaseous dipositive ions).
What is enthalpy of atomisation?
Enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state.
(For solid elements sometimes refered to as enthalpy of sublimation)
What is bond enthalpy?
Enthalpy change when one mole of covalent bonds is broken in the gaseous state.
What is first electron affinity?
Enthalpy change when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous 1- ions.
What is second electron affinity?
Enthalpy change when one mole of uninegative gaseous ions gains one mole of electrons to form one mole of gaseous 2- ions.
What is enthalpy of solution?
Enthalpy change when one mole of a solute dissolves in water.
What is enthalpy of hydration?
Enthalpy change when one mole of gaseous ions become hydrated (dissolved in water).
What is the enthalpy of combustion?
Enthalpy change when 1 mole of a substance undergoes complete combustion in excess oxygen with all substances in standard states
What is the enthalpy of neutralisation?
Enthalpy change when 1 mole of water is formed from its ions in dilute solution
Whats the pefect ionic model
when the bonding in the compound is 100% ionic
the ions are regarded as perfect spheres and are not distorted
What causes distortian in the perfect ionic model
when a cation distorts a anion so there is covalent character
no longer spherical
Cations that are small and highly charged are better at distotian
Anions that are large and highly charged are better at being distorted as electrons are further away from the nucleus so less attraction so more easily drawn way
How can covalent character be calculated
The difference between the theoretical lattice enthalpy and the real (using born harber cycle). The greater the difference the greater the covalent character
What is entropy?
The measure of disorder in a system. The more disordered the greater the entropy
The increase in entropy in states of matter
If a partice vibrates or moves around more than aother it will have greater entropy
gas then liquids then solids
Entropy increases in dissolving
ions spread in solutions have more disorder than when in fixed positions so solutions have higher entropy then solids
Enthalpy increase in mixtures
mixtures have higher entropy then pure substances as ere are more different waays particles can be arranged increaseing disorder
Order cystals structures from having the lowest enthalpy to the highest
Macromoleular
giant metallic lattice
Giant ionic lattice
Simple molecular
Gibbs free energy equation
/\G = //H - // T//S
remember to convert //s unit from J to KJ
when is a reaction feaasible in reagrds to //G
when its less then or equal to 0
Y=mx+c the gibbs equation
//G = -//s(K) + //H
Enthalpy of hydrogenation
The enthalpy change when 1 mol of unsaturated compound reacts with an excess of hydrogen to become fully saturated
