Gen chem- Uworld
Delta G= -RTlnKeq Keq= e^(-delta G/RT) If delta G is negative, is Keq less/greater than 1 or equal to zero?
-(-delta G) makes it positive, then exponent term e is positive and that make Keq >1, eqlb favor products. Note: e^0=1 e^1= e= 2.71
Ksp of CuF2 is 1.6x10^-6. Ksp of BaF2 is 3.0x10^-6. Which explain why precipitating CuF2 is better choice for separation procedure?
-CuF2 is LESS soluble and more responsive to small changes in common ion conc. Higher Ksp means higher solubility. Here, CuF2 has lower Ksp (less soluble) than BaF2. Ksp= [A+2][X-], has inverse relationship. If Ksp is small, then small changes to [A+2] or [X-] have a much larger impact than if Ksp were large. -there are FEWER moles of CuF2 to remove from the soln than moles of BaF2. F2 is the same, so compared molar mass of Cu vs. Ba. Cu has less mass. -precipitating BaF2 require a greater number of common ions to be added to the solution. Vs. not helping adding F- as common ion would cause CuF2 to precipitate. But it would also cause BaF2 to ppt.
Changing what factors can alter the experiment? Changing what factor not?
-adding a inhibitor will decrease frequency of collision -using a higher concentration of reactants will increase frequency of collision, increase rate of rxn and amount of heat produced -increase initial temp result in a greater number of molecular collisions vs. changing catalyst's cation from Na+ to K+ will not change concentration of I- or conc of H2O2- not change freq of collisions. Will not affect the heat evolved.
cm^3 to mL
1 cm^3 = 1 mL
What is mass of water necessary to generate 11.2L of hydrogen gas if calcium metal reacts with water at STP?
18g of water Ca + 2H20 -> Ca(OH)2 + H2 11.2L H2 x (1 mol gas/22.4L) x (2mol H20/1molH2) x (18.02 gH20/1 molH20)= 18g H20. don't forget to use 1 mol gas/22.4L and the mole ration from the equation.
Pure Water at 25°C, conc of a saturated solution of CuF2 is 7.4 x 10^-3M. If measured at same temp, what's the conc. Of a saturated solution of CuF2 in aqueous 0.2M NaF?
A: 4.0 x 10^-5M CuF2 <-> Cu+2 (aq) + 2F-(aq) initial: excess <-> 0, (0+ 0.2). 0 from CuF2 and 0.2 from NaF change: -x <-> +x, +2x eqlb: excess -x <-> +x, (0.2 + 2x) if x is small, can assume 0.2+2x is 0.2 Ksp= [Cu+2][F-]^2= x * (0.2)^2 Ionic cmpd placed in water, composite ions will dissociate to some extent and establish an eqlb. Ksp: solubility product. If a solution contains 2 salts that have an "ion in common", the common ion supplied by 1 salt produces a common ion effect that stresses product side of eqlb of other salts and shifts eqlb to the left. Hence, both salts the solubilities decrease. CuF2 (s) <-> Cu+2 + 2F- NaF(s) <-> Na+ + F- when dissolving CuF2 in 0.2 M NaF, initially there's no Cu+2 or F- in solution from CuF2, but there is 0.2M F- from NaF. If amount of CuF2 eventually dissolves, changes n eqlb conc evaluated from table.
If want to separate an aqueous mixture of CuF2 and BaF2 (Ksp= 3x10^-6) by precipitous CuF2 from the solution. What should be added to solution to perform the separation?
A: Cu(N03)2 If added Cu(No3)2, Cu+2 ions can be introduced into soln. Increased Cu+2 conc disturbs product side and cause it shift toward the reactants, will cause CuF2 to precipitate. Vs. not helping -adding NaF, cause an increase in fluoride ion conc. B/c CuF2 and BaF2 both have fluoride anions, this decrease solubility of both cmpds and cause some of both to precipitate together, making separation harder. -adding Ba(NO3)2 would increase Ba+2 ion conc. Common ion effect cause BaF2 to precipitate rather than CuF2. -adding water; not help in precipitating either cmpds. This have opposite effect, b/c more of the cmpds can dissolve with an increased volume of water.
If decreased the temperature, would the cylinder solution increase or not, and the object would float or sink?
A: Cylinder solution density will increase, and the glass bulb will float. Materials expand when heated and contracted when cooled. Object float if its density is less than that of liquid, but sink its density is greater. As temp of solution decrease, density of solution INCREASES. B/c glass bulb acts like an isolated system, its density changes very litte.
Which isoelectronic species is the smallest ion? Na+, F-, Mg+2, O-2
A: Mg+2 All these are isoelectronic (same number of electrons), but b/c the number of PROTONS is different in each ion, e- in each ion experiences a different Z-eff. Hence, in an isoelectronic series: ***ionic radii decrease with increasing atomic number**. B/c magnesium has highest atomic number (biggest number of protons) in isoelectronic series, Z-eff is greatest in Mg ion, making it the smallest within given species.
Which would assist in separating an aqueous mixture of CuCl2 and CuSo4 at 90C? Look at graph: temp (x-axis) and solubility (y-axis). CuCl2 has a higher solubility than CuS04.
A: add Na2SO4 and cool it 5C Add So4- and lower temp ppt CuSo4. using common ion effect, adding NaS04 would introduce SO4- that would bind to ion Cu+ already present to form CuSo4. Lower temp: seen on graph, solubility decrease as temp decreases. But solubility of CuS04 decreases greater extent. Vs. not helpful -adding Cu(no3)2: this increase conc of Cu+2 and both species has that. Although CuSo4 would ppt to a greater (due to less soluble), some CuCl2 wold still ppt and result in a ppt mixture. -lower pH by adding acid. Cl- is not basic enough to react with acid and shift solubility eqlb of CuCl2, and any S04- reacting with H+ to form HSo4- would interfere with precipitation of CuS04 by shifting eqlb to right and cause more CuS04 to dissolve.
2g of aluminum foil added to 500ml of CuCl2 solution, rxn: 2Cl(s) + 3 CuCl2(aq) -> 2AlCl3(aq) + 3Cu(s). limiting reagent?
A: aluminum
Nernst eqt: stating that concentration cell has a potential E of 0.089, E= ....log [x]anode/[y]cathode, asking concentration is greater at anode or cathode and direction of electron flow
A: concentration is greater at cathode, and e- flow from anode to cathode. If conc were greater at anode, ratio of [x]anode/[y]cathode would be greater than 1 and log term would be positive, causing final value of E to be negative (small minus big).. Measured potential E is positive, ion conc must have ratio less than 1 so log is negative. A negative log multiplied by negative constant result in positive E.
If excess methylamine (Ch3Nh2) added to a saturated aqueous CuF2 solution, amount of CuF2 that dissolves will: increase, decrease, same?
A: increase Psg: copper ions form an affinity to form coordinate bonds with available lone pair electrons of nitrogen atoms in amines. This results in a shift toward products forming more Cu+2.
If experiment utilize a reaction that reduces Cl04- to Cl03-. Which experimental approach will make reduction of Cl04- more favorable?
A: perform the reaction under ACIDIC conditions. Using Frost diagram, compare the slope of 2 species mentioned with pH 0 and pH14. The higher energy species is more favorable toward reduction with steepest positive slope. The couple with pH 0 has more steepest slope/greater value.
What does coordination number in a metal complexes refer to?
A: the number of coordinate bonds formed. Ex: Cu form 4 coordinate bonds to 4 other substituents
Assuming they're homogenous catalysts in the same phase as reactants, the type of catalyst then affect the rate or heat of reaction?
Affect only the RATE of rxn, not heat of rxn.
How does London dispersion intxns look like?
Between nonpolar amino acids side chains Ex: multiple hydrocarbons chains next to each other
What is combustion reaction?
Burning of a fuel ie. Hydrocarbon, alcohol, etc in presence of oxygen to form carbon dioxide and water.
Combination rxn vs. decomposition rxn
Comb: 2 elements are joined to form 1 new stable cmpd Decom: 1 cmpd is breaking down into multiple elements
What is activation energy? What is its sign always?
E-a: minimum amount of energy required to initiate a reaction. Difference btwn energy of transition state and nerdy of reactants E-a= E-transition state - E-reactants **E-a always POSITIVE.
Does a negative slope m on Van't Hoff plot indicates exothermic or endothermic rxn?
Endothermic rxn
How to evaluate table of rate laws and reaction orders.
General rate law: Rate= k[A]^m[B]^n k is rate constant Look for 2 rows, to find A: keep B same, different values of A. Determine if conc is doubled or quadrupled and if initial rate also increase by same or different factor. Do the same for B: keep A same, different values for B. m + n= determine the reaction order. 1 + 1 = second order. Rate= k[A][B] **if doubling reagent's concentration doubles the reaction rate, rxn is first-order wrt that reagent. **if doubling concentration quadruples the rate, rxn is second order. **if doubling concentration make rxn rate eight times greater, rxn is 3rd order.
What is the space between reactants and compounds referred as? what conditions needed for exergonic or endergonic?
Gibbs free energy, delta G. G= G-products - G-reactants Energy of products < Energy of reactants, get negative G, exergonic- energy is released vs. energy of products > energy of reactants, get positive G, endergonic (energy is required/consumed)
Decomposition of H2C03 yield what products?
H20(l) + CO2(g)
Ka and pKa in relation to acid strength
High Ka and low pKa: stronger acid Ka and pKa are inverse.
Homogenous catalysis vs. heterogenous catalyst
Homo: same phase as reactant. Hetero: different phase. Usually solids interacting with reactants that are either liquids or gases. Reactants adsorb onto solid catalyst surface, either promote interaction of 2 reactants or weaken the bonds in reactants. Both increase reaction rate by stabilizing high energy TS. **having more surface area of a catalyst increase rate of reaction.
How is hydrogen bond and dipole-dipole intxns related?
Hydrogen bond is a special type/subset of dipole-dipole intxns. H is covalently bonded to highly EN elements ie. F,O,N. vs. Other types of dipole dipole doesn't involve H, FON, but attraction between any partially positive and partially negative atom.
Which alkali metal is the least reactive based on first ionization energy?
IE= energy required to remove a valence electron going up the column, Li requires higher energy so it would be least reactive
Molecule with low solubility in water due to high nonpolar hydrocarbon are subjected to titration. What steps needed taken?
It needs to be fully dissolved before it can be measured. Since its an acid, needs to dissolve it in BASE which will convert carboxylic acid group into highly polar ionic salts with higher aqueous solubility. Once dissolved, carboxylates anions is titrated with an ACID and an indicator.
Qs give complicated reaction equation. If 6 moles of electrons required to reduce 1 mole of Cl03-, how many electrons are reqd to completely reduce all of Cl03- ions present in 250ml of a 4.8 M Cl03- solution?
It's misleading thinking that we have to do mol to mol ratio from the reaction. Treat it simple use all the values given. 250ml x (1L/1000ml) x (mol/L) x (6 mol e-/1 mol Cl03-) = mol of electrons note: 6 mol e-/1 mol Cl03- is considered as mole ratio.
Kinetic product vs. thermodynamic product?
Kinetic product: cmpd with LOWEST energy transition state forms fastest. Thermo: cmpd has a HIGHER energy transition state, but it is more stable structure (lowest energy on y-axis)
How to dissolve the amount of insoluble reactants to where can increase one product by disturbing the conc of the other product?
Le Chatelier's principle: changing the pH of a soln enhance the solubility of salt that have an acidic or basic ion. If some of products are removed, eqlb will shift to form more of products. Look at the product ion and see if it's an acid or basic. Ex: ion is basic, which can react with acids. Hence, by adding ie. Nitric acid (source of H+) it will cause F- to bind with H+ to form HF, H+ + F- <-> HF. This cause a decrease in F- con. this will disrupt eqlb causing a shift toward the products to form more F-. Then more CuF2 (reactants) to dissolve/dec and Cu+2 conc to increase when the system trying to compensate for the loss of F- from adding nitric acid. Vs. not helping: -adding more OH- ion could disturb eqlb by reacting with Cu+2 ion to form Cu(OH)2. But very small Ksp of cu(oh)2 indicates it's very insoluble in water. But then not much CuF2 dissolves and lower the cu+2 conc. -adding KF, will increase F- conc. Due to common ion effect, this shift toward reactants which results in an increase in CuF2 and not it actually dissolving, and also lower amount of Cu2. -evaporating. Amount of its solubility stay same. As water evaporates, some dissolved CuF2 will precipitate, but Cu+2 conc/volume remain unchanged.
What does a low electron affinity indicates? which alkali metal has the low EA?
Low EA ie Cs means weakest electron affinity and least likely to accept an additional electron
What does catalyst change and not change?
Lower activation energy to increase the reaction rate. But it does not affect the AMOUNT OF PRODUCTS produced or enthalpy delta H (heat of rxn) remain same.
On periodic table, metals have a lower or higher first ionization energy than nonmetals?
Metals have LOWER ionization energy than nonmetals. First IE tend to increase across a row and decrease down a column. Same is true for second IE except when second electron being removed is not a valence electron. Except: second IE of Na (group 1) is much higher than that of Mg (group 2) bc Na has only 1 valence e- and removing a second electron from Na requires the loss of a CORE electron. The availability of a second valence e- gives Mg (group 2) the lowest second IE.
Does the identity of the catalyst affect heat of reaction assuming using same amount of substrate?
No. They both will result in same change in temperature.
Asking for standard potential E for a particular half-reaction. Cl03- .... -> HCl02. Using Frost diagram to predict slope that equate to E
Psg: slope of a line segment joining 2 species on a Frost diagram equal the standard reduction potential for the couple. Identify which 2 species are talking about then solve fo slope. E= slope= (y2-y1)/(x2-x1)= V
If the reactants have more energy than the products, what happened to delta H, is it endo or exothermic rxn? If reactants are lower in energy than the products, what is delta H, endo or exo?
Reactants > Products: delta H is negative, exothermic and releases energy. Reactants < products: delta H is positive, endothermic and requires energy delta H= E-products - E-reactants
What groups on period table are considered representative elements?
Representative elements aka main group elements, Group 1-2, Groups 13-18. Excluding the transition metals. Found in s and p-block
Single replacement reaction vs. double replacement rxn
Single: only 1 atom is swabbed with another Double: 2 swabs
How to read Frost diagram to determine rxns unstable toward disproportionation
Species that are above gradient line likely to disproportionate. So species below line unlikely to disproportionate. Gradient line: draws a line connecting 3 species. Disproportionation rxn: a redox rxn in both oxidation and reduction occur with atoms of SAME ELEMENT. Its tendency for disprop can be evaluated graphically.
What's the rate limiting step in reaction rate graph?
The initial step with largest energy barrier/large Ea is the slowest step that determines the rate. vs. Smaller energy barriers -faster steps -no impact on rate
Will van der waals intxn decrease, increase or same if a protein variant is made that replaces valine with alanine?
Van der waals will decrease b/c there will be fewer hydrocarbons units in side chain. Van der waals- exhibit a weak mutual attraction. It's forces tend to be more pronounced in LARGER molecules b/c larger molecules have a larger electron cloud and are more polarizable/polar and have stronger van forces.
What happened to the activation energy of the first catalyst when the second one is added?
activation energy of first catalyst is decreased bc the second catalyst stabilizes the transition state of reaction.
Ionic Radius Trend
decreases across a period and increases down a group. compared to neutral atom of a given element: its cation is smaller but its anion is larger. Losing e- to form cation + causing remaining electrons to experience a greater effective nuclear charge, Z-eff pulling electrons closer to nucleus. Vs. gaining e- to form an anion produces greater repulsion and nuclear shielding, lesser Z-eff, which pushes electrons farther from nucleus.
salt bridges (ionic interactions) Interaction are formed between what kinds of amino acids?
the attraction formed between a carboxylate ion on one amino acid's side chain with the protonated amine on a second amino acid's side chain. 2 charged (positively charged and negatively charged) R groups ie Asp and Lys form an ion-ion intxns known as a salt bridg, a type of ionic bond.
