thermodynamics Flashcards
what is the enthalpy of formation?
enthalpy change when one mole of a substance is formed from its elements with all substances in their standards states
what is enthalpy of combustion?
enthalpy change when one mole of a substance is burned in excess oxygen with all substances in their standard states
what is enthalpy of neutralisation?
enthalpy change when one mole of water is formed in a reaction between an acid and an alkali under standard conditions
what is ionisation enthalpy?
first ionisation energy is the enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions
what is electron affinity?
first electron affinity is the enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions
what is enthalpy of atomisation?
enthalpy change when one mole of gaseous atoms is produced from an element in its standard state
what is hydration enthalpy?
enthalpy change when one mole of gaseous ions becomes hydrated - dissolved in water
what is enthalpy of solution?
enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other
what is bond dissociation enthalpy?
enthalpy change when one mole of covalent bonds is broken in the gaseous state
what is lattice enthalpy of formation?
enthalpy change when one mole of a solid ionic compound is formed from its ions in the gas phase
what is lattice enthalpy of dissociation?
enthalpy change when one mole of a solid ionic compound is broken up into its ions in the gas phase
what is enthalpy of vaporisation?
enthalpy change when one mole of a liquid is turned into a gas
what are the two ways of calculating lattice enthalpy values?
experimental and theoretical
how is the theoretical value calculated?
considering the size, charge and arrangement of ions
suggests the ions are perfect spheres
which is the real lattice enthalpy value?
the experimental value
what makes ions have covalent character?
if there is distortion of the ions as this means they are not perfectly spherical
what are the characteristics of compounds that have some covalent character?
they are insoluble in water and have lower melting points than expected and electrical conductivity may be lower than expected
what does a big difference between the experimental and theoretical values mean?
the greater the difference is, the greater the covalent character of the compound
what does the magnitude of lattice enthalpy show?
indicates the overall strength of the ionic bonding
what does the arrow structure look like for working out the enthalpy of solution?
gas ions
^ ^
formation / \hydration
/ \
ionic solid ————-> dissolved ions
solution
what is entropy a measure of?
disorder
what is the symbol for entropy?
(S)
how can you increase entropy the most?
by changing state
what factors affect entropy?
— physical state
— dissolution
— number of particles
how do you calculate the change in entropy?
change in entropy = ((S) of products) - ((S) of reactants)
what does a +ve entropy value show?
there is an increase in entropy`
what is the equation for /\G?
/\G = /\H - (T x (/\S/1000)
what value does /\G have to be to mean the reaction is feasible?
/\G must be negative for the reaction to be feasible
when there is a change of state, what does /\G = ?
/\G = 0 when there is a change in state
how do you work out the temperature at which a reaction is feasible?
T = /\H / (/\S / 1000)
