oceans Flashcards
calculation for entropy change of the system
entropy of products - entropy of reactants
calculation for entropy change of the surroundings
- delta H / Temperature (in K)
calculation for total entropy change
entropy of system + entropy of surroundings
calculation for working out minimum temperature of reaction (T at which total entropy change = 0)
Tmin = delta H / entropy of system
entropy definition
the measure of disorder / number of ways of arranging particles
relationship between total entropy change and reaction feasibility
if total entropy change is positive, reaction is feasible
lattice enthalpy meaning
the enthalpy change when 1 mole of an ionic solid is formed from its gaseous ions
features of change in lattice enthalpy
- always negative (exothermic)
- more negative = stronger ionic bond
- more negative with higher ionic charge (stronger attraction) and smaller ionic radius (ions closer together) => higher charge density
change in hydration enthalpy meaning
the enthalpy change when an aqueous solution is formed from one mole of gaseous ions
features of change in hydration enthalpy
- always negative (exothermic)
- more negative = stronger ion-dipole forces
- more negative with higher ionic charge and smaller ionic radius => higher charge density
enthalpy change of solution meaning
the enthalpy change when one mole of a solute is dissolved to infinite dilution
feature of enthalpy change of solution
positive or negative
calculating enthalpy change of solution (formula)
enthalpy change of solution = enthalpy change of hydration - change in lattice enthalpy
calculating enthalpy change of solution (practical)
a. q (J) = mass of solution x shc of water x change in temperature
b. moles of salt = mass / Mr
c. enthalpy change of solution = -q (kJ) / moles of salt
enthalpy change of solution practical process (and method for investigating the dissolving of salts)
- measure volume of water using a measuring cylinder
- use and insulated cup and lid
- measure the initial temperature
- add solid salt and measure the final temperature when temperature stops changing
greenhouse effect
-solar energy reaching earth is UV
- earth absorbs some of this UV, heating up and emitting IR
- greenhouse gases (e.g. CO2 and methane) in troposphere absorb some of this IR in the IR window
- absorption of IR by greenhouse gas molecules increases the vibrational energy o their bands the energy is transferred to other molecules by collisions, thus increasing their kinetic energy and raising temperature
- greenhouse gas molecules also remit some o the absorbed IR in all directions -> some of it heats up the earth
- increased concentrations of greenhouse gases leads to enhanced greenhouse effect
what is the IR window
a part of the spectrum where water doesn’t absorb a greenhouse gas
what is Ksp
the solubility product
Ksp expression
Ksp = [product 1 +] [product 2 -]
precipitation formation and Ksp
a precipitate will form when the product of the concentration of ions is greater than Ksp
calculation for pKa
pKa = -log10 (Ka)
calculation for pH
pH = -log10 [H+]
calculation for [H+] (from pH)
[H+] = 10 ^ -pH
ph calculation for strong acids
[H+] = [acid]
unless [H+] = 2 x [H2SO4]
assumption of pH calculation for strong acids
assumes complete dissociation into ions
pH calculation for weak acids
[H+] = square root of (Ka x [acid])
calculation for Ka for weak acids
Ka = [H+]^2 / [acid]
assumptions for pH calculation for weak acids
- [H+] = [A-]
- [HAeq] = [HAinit]
pH calculation for strong alkalis
[H+] = Kw / [OH-]
assumption for pH calculation of strong alkalis
assumes complete dissociation itno ions
Ka calculation for buffers
Ka = [H+] x [salt]/[acid]
[H+] calculation for buffers
[H+] = Ka x [acid]/[salt]
assumptions for pH calculations for buffers
- [A-] = [salt]
- [HAeq] = [acid]
strong acid definition
acid that fully dissociates into ions in a solution
how do buffers work when you add an acid
HA <==> H+ + A-
increased [H+]
equilibrium shifts to left (H+ reacts with A-)
[H+] and pH are restored
need high concentration of [A-] for H+ to react with
how do buffers work when you add an alkali
HA <==> H+ + A-
decreased [H+]
equilibrium shifts to the right (HA forms H+ and A-)
[H+] and pH are restored
acid definition
proton donors
base definition
proton acceptors
relationship between acid strength and Ka/pKa
stronger acids have a higher Ka and a lower pKa
conjugate acid meaning
formed when a proton is added to a base
conjugate base meaning
formed when a proton is removed from an acid
weak acid meaning
does not dissociate completely in water
forms some H+ ions but there is still unreacted acid in the solution
factors determining the relative solubility of a solute in aqueous and non-aqueous solvents
- when a solute dissolves, the solute and solvent bonds break and new ones are formed
- usually substances won’t dissolve if the broken bonds are stronger than the new ones
- solvents can be polar or non-polar
ionic substances + dissolving
only usually dissolve in polar solvents, creating an aqueous solution
because
- the H atoms in water have a positive partial charge and the O atoms have a partial negative charge
- the ions bond to these dipoles to form ion-dipole bonds
- this causes the ions to leave the ionic lattice, and they become randomly distributed
all lattices which can be pulled apart by the ion-dipole bonds are double
covalent substances and dissolving
usually intermolecular bonds between covalent substances are weak
similarly, non-polar solvent also have weak id-id bonds because the forces are similar, most covalent substances will dissolve in non-polar solvents
in polar solvents, the H bonds between water molecules are much stronger than the bonds that would form if the substance dissolved so most covalent substances are not soluble in polar solvents
hydrated ions definition
an ion that is surrounded by its own shell of water molecules
factors affecting entropy
- gases have more entropy than l and s, liquids have more entropy than s
- more complicated molecules have higher entropy
- mixtures have more entropy than pure liquids
strong base definition
nearly completely dissociate in water to form OH- ions
