oceans Flashcards
give a reason why a substance might not dissolve
bonds to be broken are stronger than bonds to be made
what interactions form between an ion and a polar solvent?
ion-dipole interactions
define standard lattice enthalpy
the enthalpy change when 1 mole of an ionic lattice is formed from its gaseous ions under standard conditions
define enthalpy change of hydration
enthalpy change when 1 mole of aqueous ions is formed from gaseous ions
define enthalpy change of solution
enthalpy change when 1 mole of ionic substance dissolves in enough solvent to form an infinitely dilute solution
how is charge density found?
charge/radius
how does charge density affect lattice enthalpy?
ions with a higher charge density are better at attracting each other in a lattice; more exothermic lattice enthalpy
how does charge density affect enthalpy of hydration?
ions with higher charge densities are better at attracting water molecules; more exothermic
what is entropy?
a measure of the number of ways that particles can be arranged, and the number of ways energy can be shared out between them
list the factors which affect amount of entropy present
- physical state
- amount of energy
- number of moles
what is the expression for total entropy change?
delta(tot)S= delta(sys)S + delta(surr)S
how do you calculate entropy change of system? delta(sys)S
S(products) - S(reactants)
how do you calculate entropy change of surroundings? delta(surr)S
-deltaH/T
remember deltaH must be in Jmol-1 NOT Kjmol-1
what is a feasible reaction, and when is a reaction feasible in terms of delta(tot)S?
- a feasible reaction is one that will carry on until completion without energy being supplied
- total entropy change must be positive or zero
what is solubility?
the maximum amount of solid which will dissolve in a certain solvent
what is Ksp?
the equilibrium constant for a saturated solution of a sparingly soluble solid
what is meant by the term ‘conjugate pair’?
the conjugate base of an acid is formed when the acid donates a proton
an equilibrium with conjugate pairs is set up the base dissolves in water
what is the bronsted-lowry definition of a base
proton acceptors; accepts a proton from acid
what is a neutral solution?
one which had [H+] = [OH-]
how do you calculate pH?
-log10 [H+]
how do you calculate [H+] from pH?
10^-pH
how does water act as an acid and a base?
acts as an acid by donating a proton, and as a base by accepting one
how do you calculate Ka for a weak acid?
Ka= [H+]^2/[HA]
how do you convert pKa to Ka?
10^-pka
what is a buffer?
a buffer is a solution that resists changes in pH when small amounts of acid or base are added
what are the two types of buffer?
acidic and alkaline
how do acidic buffers work?
they are made by mixing a weak acid with one of its salts
provides a solution with undissociated acid molecules and lots of salt molecules
equilibrium shifts to oppose a change
how does equilibrium alter when a small amount of acid is added to a buffer?
- [H+] increases
- equilibrium shifts left
suggest two uses for buffers
- shampoo
- biological washing powder
what are the assumptions you make when you calculate the pH of a buffer
- the salt is fully dissociated
- weak acid is only slightly dissociated, the equilibrium concentration is the same as its initial concentration
how do greenhouse gases transfer energy?
- they absorb IR which makes bonds vibrate
- extra vibrational energy is passed on to other molecules in the air by collisions
what is the expression for Ka of water?
H20 = H+ + OH- then kw= [H+][OH-]
why can H2O be removed from the expression for kw of water?
concentration of water is effectively constant, because water is present in excess/position of equilibrium lies far to the left
what is defined as an acidic solution?
one in which [H+] > [OH-]
what is defined as an alkaline solution?
one in which [H+] < [OH-]
what assumptions do you make about buffer solutions?
1- all the A- ions come from the salt
2-almost all the HA molecules put into the buffer remain unchanged
why is the pH of a buffer not affected by dilution?
when you add water, the concentrations of both the acid and the salt are reduced equally. the proportion remains the same
what bonds are broken and made when a substance is dissolved?
bonds between solute broken, bonds between solute and solvent made
how do you calculate the temperature at which a reaction can happen?
deltaH/deltasysS
