Thermodynamics Flashcards
define enthalpy change
amount of heat taken in or given out at constant pressure during any physical or chemical change
define standard enthalpy change
change in enthalpy when reactants in their standard states form products that are also in their standard states
define standard state
the state at a given temperature in its pure most stable form at 100kPa
when do exothermic changes occur
when forces of attraction operate
when do endothermic changes occur
when forces must be overcome/broken
define enthalpy of formation
enthalpy change when 1 mol of a substance is formed from its constituent elements with all substances in their standard states
define enthalpy of combustion
enthalpy change when 1 mol of substance undergoes complete combustion in O2 with all substances in their standard states
define enthalpy of neutralisation
enthalpy change when 1 mol of water is formed in a reaction between an acid and an alkali under standard conditions
define enthalpy of first ionisation
enthalpy change when each atom in 1 mol of gaseous atoms loses one electron to form one mol of gaseous 1+ ions
define enthalpy of second ionisation
enthalpy change when each ion in 1 mol of gaseous 1+ ions loses one electron to form one mol of gaseous 2+ ions
define enthalpy of first electron affinity
enthalpy change when each atom in 1 mol of gaseous atoms gains one electron to form one mol of gaseous 1- ions
define enthalpy of second electron affinity
enthalpy change when each atom in one mol of gaseous 1- ions gains one electron to form one mol of gaseous 2- ions
define enthalpy of atomisation
enthalpy change when one mol of gaseous atoms is produced from an element in its standard state
define hydration enthalpy
enthalpy change when 1 mol of gaseous ions become hydrated ( dissolved in water)
define enthalpy of solution
enthalpy change when 1 mol of ionic solid dissolves in amount of water large enough that dissolved ions are well separated and do not interact with each other
define bond dissociation enthalpy
enthalpy change when 1 mol of covalent bonds are broken in the gaseous state
define lattice enthalpy of formation
enthalpy change when 1 mol of a solid ionic compound is formed from its constituent ions in the gaseous phase
define lattice enthalpy of dissociation
enthalpy change when 1 mol of a solid ionic compound is broken up into its constituent ions in the gas phase
define enthalpy of vaporisation
enthalpy change when 1 mol of liquid is turned into gas
define enthalpy of fusion
enthalpy change when 1 mol of a solid is turned into a liquid
is enthalpy of formation endo of exothermic
mostly exothermic
is enthalpy of combustion endo or exothermic
exothermic
is enthalpy of neutralisation exo or endothermic
exothermic
is enthalpy of ionisation endo or exothermic
endothermic
is enthalpy of first electron affinity endo or exothermic
exothermic
is enthalpy of second electron affinity endo or exothermic
endothermic
is enthalpy of atomisation endo or exothermic
endothermic
is enthalpy of hydration endo or exothermic
exothermic
is enthalpy of solution endo or exothermic
varies
is bond dissociation enthalpy endo or exothermic
endothermic
is lattice enthalpy of formation endo or exothermic
exothermic
is lattice enthalpy of dissociation exo or endothermic
endothermic
is enthalpy of vaporisation endo or exothermic
endothermic
is enthalpy of fusion endo or exothermic
endothermic
what unknown enthalpy does a born-Haber cycle usually calculate
lattice enthalpy
common mistakes to make in Born-Haber cycles
using wrong enthalpy changes
not multiplying by molar amounts
not taking care with signs
what does enthalpy of formation equal in most Born-Haber cycles
sum of all other enthalpy values
what do theoretical values for lattice enthalpies assume
perfect ionic model - all ions in an ionic compound are perfectly spherical
are positive ions better at distorting negative ions when they’re larger or smaller, and with a higher or lower charge
small. higher charge.
are negative ions easier to distort when they’re larger or smaller, and a higher or lower
larger and higher charge
are ionic compounds with covalent characters more or less soluble in water
less soluble
do ionic compounds with covalent characters have a higher or lower than expected melting point
lower than expected
do ionic compounds with covalent character have higher or lower electrical conductivity than expected
lower than expected
define magnitude of lattice enthalpy
overall strength of ionic bonding
what does the difference between experimental and theoretical values in Born-Haber calculations mean
the larger the difference the more covalent character the ions possess
are water molecules polar or nonpolar
polar
is water attracted to anions, cations or neither
anions and cations
is the hydration enthalpy larger or smaller for an ion with a higher charge-to-size ratio
larger
what is entropy a measure of
the amount of disorder in a system
when is the entropy value always zero
at 0K in a perfectly ordered crystal
is enthalpy of the universe always increasing or decreasing
increasing
what makes entropy increase
increase in temperature
from solid to liquid to gas
from simple to more complex molecules
define feasible (spontaneous) change
one that has a natural tendency to occur without being driven by external influences
at what free Gibbs energy value is a reaction at equilibrium
0
at what free Gibbs value is a reaction feasible
deltaG
how to find a feasible temperature at which a reaction can happen
set the free Gibbs value to 0 and solve for T
Gibbs free energy equation symbol equation
deltaG = deltaH - TdeltaS
acronym???? to remember Gibbs free energy equation
Grapes Have Tiny Seeds
word equation for Gibbs free energy
Gibbs free energy change = enthalpy change - temperature X entropy change
units for numbers used in Gibbs free energy equation
Gibbs free energy change in kJ/mol
enthalpy change in kJ/mol
temperature in Kelvin
entropy change in J/K/mol
general graphical equation of Gibbs free energy
y = mx+c
