Oceans Flashcards
enthalpy change of solution
the energy change when a solid dissolves in solution
enthalpy change of hydration of ions
the enthalpy change for the production of a solution of ions from one mole of gaseous ions
lattice enthalpy
the enthalpy change when one mole of solid is formed by the coming together of separate ions (gaseous to solid state)
ionic charge + ionic radii affecting lattice enthalpy
ionic charge - ions attract one another more strongly
ionic radius - ions can come closer together
the more negative the lattice enthalpy..
the more insoluble the solid
what is the sign of lattice enthalpy
negative because it is always exothermic because bonds are formed
describe ion-dipole interactions
Charges on the water molecules are attracted to charges on the ions. the ions are separated from the lattice by water molecules and are now in solution/are hydrated
The stronger the binding of the water molecules to the ions..
the more extensively hydrated the ions are
how does ionic radius and charge density affect enthalpy of hydration
The smaller, higher charged ions can get closer to water molecules and attract them more strongly so more energy is given out when bonds form so enthalpy of hydration is more negative. This also makes the hydrated ion larger.
sign of hydration enthalpy
negative, it is exothermic because bonds are made
Enthalpy change of solution is the difference between..
that of hydration of ions and that of the lattice enthalpy
sign of enthalpy for breaking the lattice
positive because negative lattice enthalpy is the change when the lattice is created
If the enthalpy of solution is slightly positive..
the ionic solute can still dissolve despite being energetically unfavourable, as long as entropy increases
effect on entropy when a solute dissolves
entropy increases because it becomes more disordered
explain why ionic solids are insoluble in non polar solvents
there are no regions of positive/negative charge so they cannot interact to form bonds. Enthalpy of solution is too positive for the ions to dissolve as a result.
normal greenhouse effect
The sun emits mainly UV and visible radiation, of which some is absorbed by earth and its atmosphere and the rest is reflected into outer space
The earth is now heated with this absorbed radiation
It radiates some of the radiation, mainly infrared
Water molecules absorb certain frequencies of radiation, the IR window is the frequencies that water does not absorb. Greenhouse gases like CO2 and CH4 absorb radiation in the IR window.
IR is absorbed by bonds in greenhouse gases causing these bonds to vibrate more
Vibrational energy is transferred to other molecules in the atmosphere, oxygen and nitrogen, by collisions
This increases the kinetic energy of molecules in the atmosphere
Some IR the molecules absorb is reemitted back towards earth to heat it further or outer space
enhanced greenhouse effect
Too much CO2 and CH4 are released due to human activity so more radiation is absorbed than reemitted so the temperature of the atmosphere is increasing, resulting in global warming.
describe the BL theory of acids and bases
Acids are proton donors, bases are proton acceptors
Once an acid has donated a base there is always the possibility that it can take back the proton, this results in acid/base pairs
define conjugate acid and conjugate base
can donate a proton, has a positive charge
can accept a proton, has a negative charge
explain why a strong acid has a weak conjugate base
the acid has a strong tendency to donate protons so the conjugate base will have a weak tendency to accept them back
strength of an acid refers to..
how powerful a proton donor it is
characteristics of weak acids
A weaker tendency to donate protons and it does not dissociate completely when dissolved in water
describe where POE is for weak and strong acids
the weaker the acid, the further left
the stronger the acid, the further right because full dissociation has occurred
characteristics of a strong acid
A stronger tendency to donate protons and it dissociates completely when dissolved in water.
what does pH measure
the concentration of hydrogen ions in solution on a logarithmic scale
in weak acids, how do you calculate pH
Ka = [H+] [A-] //// [HA]
pH = -log[H+]
what is pKa and what does the value of it suggest
-log10 Ka; useful when Ka is particularly small. The weaker the acid, the greater the value of pKa and the smaller the value for Ka
what are the two assumptions involved in calculating pH for a weak acid
[H+] = [A-] at equilibrium because they have the same number of moles.
Water is a second source of hydrogen ions but it produces a much lower number so does not cause significant inaccuracy by being neglected.
Second assumption: [HA]init = [HA]eq
This neglects the fraction of HA which has lost H+ because the fraction is very small.
Kw is
the ionisation product of water and is used for the pH of a strong alkali
what do buffers do
They maintain a constant pH when small amounts of acids/alkalis are added.
Solutions of a weak acid and its corresponding salt or of a weak base and its corresponding salt.
what are the assumptions involved in determining how buffers work
All the A- come from the salt (HA supplies very few due to weakness)
Almost all the HA molecules put in the buffer solution remain unchanged
adding acid to buffers
By adding protons, the concentration of H+ increases
The extra H+ react with A- to make more HA and H+ are effectively removed
This causes position of equilibrium to shift to the left
pH is reestablished
adding alkali to buffers
By adding OH-, concentration of H+ decreases
The protons which were used up to react with the added hydroxides to form water are replaced when HA dissociates into H+ and A-
This shifts the position of equilibrium to the right
pH is reestablished
equation for calculating pH of buffers
Ka = [H+] * [salt]////[acid]
assuming A- conc and HA conc is equal to that of the salt and acid
what is Ksp
the solubility product constant/ concentration of the ionic product at the threshold of solubility
what does Ksp represent
the conditions for equilibrium between a sparingly soluble solid and its saturated solution
if the ionic product is larger than Ksp..
a ppt will form
if the ionic product is smaller than or equal to Ksp..
everything dissolves and there will be no ppt
define entropy
the measure of the no of ways of arranging particles
order of entropy in states and purity
gas > liquid > solid
pure > solution > mixture
factors to consider for signs of entropy changes ie positive or negative
Increase or decrease of product molecules
Change in state i.e to solid or gas
total S =
system S + surroundings S
system S =
sum of S products + sum of S reactants
surroundings S =
- enthalpy change of the system //// temp in K
delta S =
overall changes in entropy
when will a reaction occur spontaneously
if total S is positive and the activation enthalpy isn’t too large
what is 0
the threshold of spontaneity
what does fewer gas molecules on the right of an exothermic reaction indicate
entropy of the system decreases and that of the surroundings increases
how does lattice enthalpy change from F- to Cl-
size of the anion increases so the ions in the attract each other less strongly
how does hydration enthalpy change from F- to Cl-
becomes less exothermic as the anion size increases and attracts water molecules less strongly
explain the colour of phenolphthalein in alkali solutions
the equilibrium shifts right because the protons are removed by reaction with hydroxide ions so the indicator is present as In- which is pink
acid is added to an ethanoate buffer
ethanoate ions from the salt react with protons to form more ethanoic acid and water so pH remains constant
alkali is added to an ethanoate buffer
additions of hydroxide removes protons but these protons lost are replaced by more dissociation of ethanoic acid so pH remains the same
