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Chem test
equilbirium
| Question | Answer |
|---|---|
| what does large Kc value mean | many products are formed |
| what does a small Kc value mean | few products are formed (more reactat) |
| equation for Q | rxn quotient = products /reactants |
| differece between K and Q | they are mathmatically the same but K is @ equilibrium while Q is at a random place (can still be @ equil) [] = K () = Q |
| given the amnount of product and ractant and the equlibrium Kc, how to determine the direction of a rxn (the direction a rxn goes until it reaches equil --> may start with more ractant or product) | write the Q expression substitute the initial concentration values in if Q < Kc then the rxn proceeds in the forward direction i Q > Kc, the rxn prceeds in the reverse direction |
| how Le Chatelier's principle relates to Q | principle: some stresses (chage in []) cause change in Q only while a T change affects K. In these casesew, the species redistributes (starts to react more aggressively in one direction) to bring Q and K back into equality |
| Kc Kp Ka Kb Kw Ksp | concentration (M) pressure (gasses) acids bases water solubility product (solutions - allows us to calculate where a solution will be saturated) |
| given the Kc, the initial concentrations, and the balanced equation, rom the equilibtium concentration | write the K expression make a ICE chart use "X" for the amount of change plug the chart values into the K expression use the quadratic formula if nessesary (if you can, take the square root of everything to avoid the formula) |
| units that you can or can't use in an ICE chart | you can use moles, M (only if the V is constant), atm (only if the V and T are constant), but you can't use grams ICe charts are based on balanced reactions and stoichiometry, so you can't use g cause every substance has a different molar mass |
| Kp formula | can use any units for P as long as they are consistant Kp = (Preact)^b/(Pprod)^a -only dependant on T |
| relationship of Kc to Kp | Kp = Kc (RT)^Δng ---> another version of ideal gas law Δng: change in gaseous moles (final moles minus intiial moles (coefficients) |
| when manipulating rxns w/ Ksp similarily to Hess's Law | if you reverse a rxn, then flip the Ksp: 1/K if you halve the coefficients in a rxn, then take the square root of K if you double the equation, then square K instead of adding the Ks like Hess's law, multiply them |
| in precipitate rxns, what are the special transition cations that only have one charge -youd don't need to put roman numerals when naming them | Ag+1, Zn+2, Au+3 |
| diatomic ion | mercury (II) = Hg+2 Mercury (I) = Hg2+2 Hg+1 doest NOT exsist |
| precipitate net equations | cationa + anion --> salt -not double arrow (althought it will eventually reach equilibrium becuase we are only talking about the initial formation of the solid/net equations show what's happening at that moment) |
| MOLEtiply | anything you have a V and molarity, multiply to get moles |
| althought the solubility rules are based on 1.0 M @ room temperature in water, we have an idea of a substances solutbility at other M becuase | if soluable: it is soluable 0.1 M and lower if ppt: it ppt 0.1 M and higher |
| equilirbium of a saturated solution | the solid will continute to dissolve, but at the same rate as it precipitates |
| Ksp expressions | -only meaningful for saturated solutions or situations involving a solid–solution equilibrium solid <--> cation (aq) + anion (aq) Ksp = [cation][anion] ALWAYS do an ICE chart (usually involves molar solubility) |
| molar solubility | number of moles of solute that dissolve in 1 liter of solution to form a saturated solution. -can NEVER be negitive -a smaller value means that ithad a lower solubility |
| under what conditions can molar solubility and solubility product constants (Ksp) be compared | only if the salts dissociate to give the same stoichiometric ratio of ions with the same charges. (1:2 and 2:4 are comarable) |
| what happens if Ksp and molar solubility can NOT be directly compared | |
| what does a big or small Ksp mean | big = it is soluable small = insoluable |
| how to convert M into g/100ml | break M into a fraction (assume 1 L per __ moles). convert moles into grams. then divide grams by 10 100ml chunks (the number of 100ml chunks in one L, AKA 10 (100ml) --> in this case, the 100ml is the units, dont put into calculations |
| solubility rules 1 and 2 | Group 1, NH4+1, NO3-, and CH3COO-1 never form precipitate (alawys soluble) -NOTE: this rule takes precedence over all other rules!!! |
| solubility rule 3 | halogens for ppt with Ag, Pb, and Hg (along with all ion versions of these, EX Pb+2, Pb+4, etc) |
| solubility rule 4 | SO4-2 forms ppt with Ag, Pb, Hg, Ca, Sr, Ba |
| solubility rule 5 | OH-1 forms ppt with everything excpet Ca, Sr, and Ba |
| solubility rule 6 | PO4-3, CrO4 -2, CO3 -2, HCO3-1, Cr2O7-2, all form precipitate |
| solubility rule 7 | S-2 all form ppt excpet with group II |
| is something is on the borderline between soluable and insoluable, what do we call it | slightly soluable |
| explain why rule five occurs | -Sr, Ca, Ba are strong bases when w/ OH. In H2O, they dissociate 100% & no solid solution equilibrium 👉 Precipitation requires a solid in equilibrium w/ ions For strong-base hydroxides, Ksp us large. Therefore, it can only precipitate > 1.0 M |
| what can determine if something will precipitate (other than what you mix together) | -how much solute you dissolve in the solvent -the more that you put in, the more likely it is to precipitate |
| everything will eventually precipitate if the concentration is too high. To be more specific than the solubility rules allow, we use ... | ion product: it is kinda like Q if IP > Ksp, ppt forms (solution contains a higher [] of ions than it can hold at equilibrium) if IP < Ksp, no ppt forms (solutions has a lower [] of ions than it can hold) if IP = Ksp, it's a saturated solution |
| with which substances is Ksp not useful | highly soluble salts dissolve almost completely, so a solid–solution equilib is uncommon (don't use Ksp) most useful for sparingly soluble salts that form saturated solutions at low [], have small Ksp and readily establish a solid ⇌ ions equilib |
| how solubility rules relate to Ksp values | -rules are based on typical Ksp values: Soluble salts have large Ksps while Insoluble salts have small Ksp -solubility rules are a simplified classification of Ksp values -values > 1 correspond to soluble salts |
| NOTE: don't use diatomics in precipitate and dissociation equations | |
| common ion effect | sometimes, two aqu solutions are mixed and there is a common ion (an ion present in both solutions being mixed) salts are less soluable in a solution where there is a common ion |
| salts | An ionic compound formed when the hydrogen ion (H⁺) of an acid is replaced by a metal ion or another positive ion (such as NH₄⁺). |
| why does a common ion lower soluability | Le Chatelier's principle -when more of an aq ion is added, the equilibrium shifts left to the reactants (the solid) and forms more precipitate |
| NOTE: you can only assume x is small in COMMON ION calculations | |
| we can take a precipitate and modify it so that it dissolves. We can do this by adding... (number 1) | a strong acid (H+) to react with basic anions ppt + strong acid --> two things that don't prcipitate according to solubility rules |
| we can take a precipitate and modify it so that it dissolves. We can do this by adding... (number 2) | a complexing agent (like NH3 or OH-) to react with metal cations (attach a metal cation with an ion) to form a soluable complex ion |
| ligand def | an ion or molecule that binds to a central metal ion by donating one or more lone pairs of electrons, forming a coordinate covalent bond. |
| What is a complex ion? | A complex ion consists of: One central metal ion (usually a transition metal) Surrounded by ligands (molecules or ions that donate electron pairs) It has at least one metal ion Plus one or more ligands (which may be neutral molecules or ions) |
| why does the formation of a complex ion dissolve precipitate | When ligands are added: They remove metal ions from solution by binding to them This causes more solid to dissolve to replace the metal ions So the precipitate disappears |
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Blessed Rectangle 10