chap 8- oceans Flashcards
what can prevent substances from dissolving
if the bonds to be broken are stronger than those that will be formed
why do ionic substances not dissolve in non polar solvents
the non polar solvents don’t interact strongly enough with ions to pull them away from an ionic lattice. the electrostatic forces between the ions are way stronger than any bonds that can form
why do covalent substances only dissolve in non polar solvents
IM bonds between covalent molecules tend to be pretty weak so can be broken by non polar solvents. don’t dissolve in polar substances because H bonds are stronger than the bonds that would form between the water and non polar solvent
what is the difference between hydration and solvation
hydration is the process of ions being surrounded by water molecules to become hydrated ions. if the solvent isn’t water though this process is called solvation
what is standard lattice enthalpy
the enthalpy change when one mole of an ionic lattice is formed from its gaseous ions under standard conditions
what is the enthalpy change of hydration
the enthalpy change when one mole of aqueous ions is formed from gaseous ions
what is the enthalpy change of solution
the enthalpy change when one mole of an ionic substance dissolves in enough solvent to form an infinitely dilute solution
how can you measure enthalpy change of a solution using an experiment
put reactants in a container, stick a themometer in and measure temp change (use polystyrene beaker and lid) then use Q=mc T
what is charge density of an ion
charge / radius
higher charge density means its better at attracting ions of the opposite charge
what is entropy
measure of the number of ways that particles can be arranged and the number of ways energy can be shared out between particles
why do particles try to increase entropy
substances like disorder and they’re more energetically stable when there’s more disorder
how does energy affect entropy
the more energy quanta a substance has the more ways they can be arranged and the greater the entropy
how does number of moles affect entropy
entropy increases as number of moles increases because there are more particles and so more ways their energy can be arranged
how do you calculate the total entropy change of reactants and products
entropy change of system + entropy change of surroundings
how do you calculate the total entropy change of a system
entropy of products - entropy of reactants
how do you calculate entropy change of the surroundings
-enthalpy change (Jmol-1) / T
what is a feasible reaction
one that once started will carry on to completion without any energy being supplied to it
what does a reaction need in order to be feasible
for the entropy change to be positive or 0
what is a saturated solution
a solution where the water has dissolved as much of the solid as it can hold and you can add extra solid but none will dissolve
what is solubility
the maximum amount of solid that will dissolve in a certain solvent (changes with temperature)
what is a sparingly soluble solid
only dissolves a little bit to give 30-100 parts solvent to 1 part solute (10-30 g dm-3 in water)
how do you work out solubility in moldm-3 from solubility in gdm-3
divide by the molar mass (M)
what is the difference between acids and bases in terms of protons
acids release protons and bases accept protons
whats a bronsted lowry acid
a proton donor that releases hydrogen ions when mixed with water and combine with the water to form hydroxonium ions (H3O+)
whats a bronsted lowry base
a proton acceptor that grabs hydrogen ions from water molecules
what is a conjugate pair
an acid and a base where the base accepts the proton from that acid and the acid donates its proton to that base
what is a neutral solution
one where H+ and OH- concentrations are equal
how do you work out pH from H+ conc
pH = -log10 (H+)
what is a monoprotic acid
each mole of acid produces one mole of hydrogen ions
how can you work out (H+) if you know the pH
10^-pH
what is Kw
a constant called the ionic product of water. units are always mol2dm-6. always has the same value for an aqueous solution at a given temperature
how do you calculate Kw
(H+)(OH-)
what is the Kw value for an aqueous solution at 298K
1x10-14 mol2dm-6
what is the value of Kw in pure water and why
Kw= (H+)^2 because in pure water there is always one H+ ion for every OH- ion
what are the units of Ka
mol dm-3
what is the general expression for Ka
Ka= (H+)2 / (HA)
what does pKa =
-log10 Ka
how do you work out Ka if you know pKa
10^-pKa
what is a buffer
a solution that resists changes in pH when small amounts of acid or base are added or its diluted
what is an acidic buffer
pH of less than 7 made by mixing a weak acid with one of its salts. Ethanoic acid and sodium ethanoate is a good example (CH3COO-Na+)
how are buffers used in respiration
blood needs to be kept at pH 7.4. its buffered using carbonic acid (H2CO3) and levels are controlled by respiration
what does the sun emit electromagnetic radiation as
visible light, UV radiation and infrared radiation
what happens when the suns radiation reaches the earths atmosphere
most of the UV and infrared is absorbed by atmospheric gases and some radiation is reflected back into space from clouds
3 main greenhouse gases
water vapour, carbon dioxide, methane
how do greenhouse gases transfer energy
they absorb IR radiation to make the bonds in the molecule vibrate more. the extra vibrational energy is passed on to other molecules in the air by collisions (transfers kinetic energy and heat)
