topic 8 and 13 enthalpy changes definitions Flashcards
where is chemical energy stores
in the bonds
change in enthalpy
heat change per mole in a reaction measure under sc
formation
change in enthalpy when 1 mole of product is formed from its elements in their standard state under sc
combustion
change in enthalpy when one mole of substance burns completely in oxygen
reaction
enthalpy change when when molar quantities as stated in equation react under sc
neutralisation
change in enthalpy when 1 mol of water is produced from an acid plus alkali reaction under sc
what might be some errors for enthalphy change of combustion
heat loss to surrounding due to radiation
incomplete combustion
not in sc
law of conservation
amount of energy in isolated system stays the same
energy cannot be destroyed or created
it can only be transferred from one store to another
difficulty when calculation change in enthalpy
high Ea
slow rate of reaction
side reactions take place
toxic products produced
how to measure enthalpy
calorimetry test
mean bond enthalpies
hess cycles
bond dissociation
enthalpy change when one mol of covalent bond is broken between two atoms with all species are in gas state
bond dissociation
enthalpy change when one mol of covalent bond is broken between two atoms with all species are in gas state
whys there varying enthapy change values when comparing using mean bond enthalpy values and true values
bc mean bond enthalpy is the average value of bond dissociation enthalpy of a particular bond over many compounds
what is born haber cycle
thermo chemical cycle showing all the enthalpy changes in involved in the formation of ionic compounds with elements starting in standard state
what affects lattice energy
size of ion and charge of ion
what is perfect ionic model
assumes ions are perfecticly spherical with charge evenl distributed throughout ion
attractions purely electrostatic
why are they not perfect
ions are not perfect spherical as polarisation ccurs so covalent character is gained
cation distrots -ve ions electron cloud due to polarisation
entropy units
J K-1 Mol-1
what is entropy at 0k
0 as particles dont move and are in max state or order
change in S(total)
change in S(system) + change in S(surrounding)
change in S(system)
sum of change in S for products - sum of change in S for reactants
change in S surrounding =
minus change in enthalpy over temp
change in enthalpy units JMol-1
gibbs free energy
change in enthalpy - (Temp x change in S(system) /1000)
as S is in J MOl-1
second gibbs free energy equation
= -R T lnK
when is a reaction feasible
when gibbs free energy is equal or less than 0
atomisation
Standard enthalpy of atomisation: Enthalpy change when 1 mole of gaseous atoms is formed from
the elements in its standard states. Always endothermic
lattic enethalpy
Standard lattice energy: Energy change when 1 mole of an ionic solid is formed from its constituent
gaseous ions under standard conditions
electron affinity
First electron affinity: the enthalpy change that takes place when one electron is added to each
atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
hyrdation
Enthalpy change of hydration : The enthalpy change when 1 mole of a gaseous ion is completely
dissolved in water under standard conditions. to infinite dilution
solution
Enthalpy change of solution : Enthalpy change when 1 mole of ionic solid completely dissolves in
water under standard conditions to form an infinitely dilute solution.