Gen Chem Class 4-5

Question 1

How do you calculate the rate laws for reactants in a data set from an experiment?

Answer 1

Question 2

what is the only variable that equilibrium constant relies on for a given reaction?

Answer 2

reaction temperature

Question 3

How do you determine the equiliubrium constant K (big K) for a given reaction?

Answer 3

Rules:

1. The coefficients for the reaction become the powers to which the concentrations are raised in the products of reactants ratio (equilibium equation)

and

2. NO SOLIDS OR PURE LIQUIDS (l) are counted in the equilibium equation! Only gases and aqueous liquids.

* equation for K is called mass-action ratio

Question 4

gaseous equilibrium uses K_p (equilibium pressure). How is it determined

Answer 4

Use pressures instead of concentration but the exponent rule applies and you still use products over reactants

Question 5

T/F: the ratio of reactants to products in a given reaction do affect the K_eq as long as temperature is held constant

Answer 5

true

Question 6

what does “Q” indicate in a ratio of products to reactants

Answer 6

Reaction quotient.

The ratio of products to reactants at an instantaneous point in time, where the ratio is not at equilibrium.

equilibrium is when Q=K_eq

Question 7

when Qeq, in which direction does the reaction proceed

Answer 7

to the right, favoring products, forward direction

*note that it does this in an effort to achieve Q=Keq even if it overshoots it at first

mnemonic: mentally align Q with products and Keq with reactants. then Q<keq>
</keq>

Question 8

when Q>Keq, in which direction does the reaction proceed

Answer 8

to the left, favoring reactants, reverse direction

*note that it does this in an effort to achieve Q=Keq even if it overshoots it at first

mnemonic: mentally align Q with products and Keq with reactants. then Q>Keq means products>>reactants (much greater than they’re supposed to be for eq)

Question 9

problem solving process that I got wrong

Answer 9

notice that you aren’t simply looking at whether the products are greater than the reactants (in this case doing that would lead you to the right answer but for the wrong reasons). Intead, for a given set of molecules in a reaction, they have a preferred ratio.. so you have to compare Q (what the ratio really is) to Keq (what the ratio should be for equilibium)

Question 10

How does chang in temperature affect the K_eq of a reaction?

Answer 10

Because heat can be treated as a product in an exothermic reaction and a reactant in an endothermic one,

consider the effect of heat the same way you would a reactant or product (depending on whether its exo or endo thermic).

If you add heat to an exothermic reaction (Ie once the rxn has reached quilibium), you are adding it to the product side (because it’s exothermic) then the reaction shifts to left to minimize the excess products and thus it favors reactants. So the opposite, lowering heat, favors the exothermic reaction (because your goal is products)

If you add heat to an endothermic reaction, heat is added to the reactant side and the reaction shifts to the right, to minimize the reactants, and products are favored so raising the temperature favors an endothermic process (because your goal is products)

Question 11

for a gaseous reaction, pressure affects K_eq. How so?

Answer 11

adding pressure to a reaction container will cause equilibrium to shift to favor the side with the fewer number of moles of gases (moles = the coefficient).

This can be done by decreasing the volume of the container.

*one special condition in which the volume increase/pressure decreases without changing the volume of the container itself is by adding an inert gas into a constant pressure container (with a piston). The inert gas will push against the piston and increase the volume of the container, therefore decrease the pressure.

*** When it comes to partial pressure….if the equilibrium constant remains the same, increase partial pressure increases solubility

Question 12

inert gases can be found where in the periodic table

Answer 12

farthest column to the right (they include all the noble gases and also some other non-noble gases that I don’t need to know)

Question 13

T/F: A catalyst has no effect on K_eq

Answer 13

true, it increases the rate of the reaction

but since Keq descibres equilibrium regardless of rate, there’s no effect on Keq

Question 14

hydration is to water as ___________ is to _________

Answer 14

solvation is to solvent

hydration is a type of solvation where the solvent is water

Question 15

what is the ionizability factor?

Answer 15

denoted by i , it tells how man ions one unit of a substance will dissociate into within a solution

for a non-ionic species, nothing breaks up into ions, so the one molecule will remain one molecule and i =1 (e.g. C₆H₁₂O₆)

NaCl will dissociate into Na+ and Cl, so i = 2

CaCl₂ will dissociate into Na+ and Cl, so i = 3

*not all ions will dissociate, it depends on what are joined together for example CaCO₃ is not soluble…. solubility rules on a different card

Question 16

T/F: some ionic compounds are stronger electrolytes than others

Answer 16

false: all ionic compounds are defined as strong electrolytes. It’s covalent compounds that are considered weak

Question 17

at a point of molar solubility for a solvent, precipitation occurs at the same rate as?/faster than?/slower than? dissolving, this is termed _____ ______

Answer 17

at the same rate

dynamic equilibrium

Question 18

when you get the weight of elements from the periodic table, in what unit should it be written?

Answer 18

g/mole

Question 19

in questions where they are asking for concentration in a solution, what are they asking for in terms of units?

Answer 19

the are asking about relative or absolute concentration of solutes. So the expression would be in terms of molarity. So in a 0.2 M solution of CaBr₂, the concentration of Br^- is 2(0.2).

Question 20

Solubility Rules for Phases

1. The solubility of solids in liquids tends to increase?/decrease? with increasing temperature
2. The solubility of gases in liquids tends to increase?/decrease? with increase temperature
3. The solubility of gases in liquids tends to increase?/decrease? with increasing pressure.

Answer 20

1. The solubility of solids in liquids tends to increase with increasing temperature
2. The solubility of gases in liquids tends to decrease with increasing temperature
3. the solubility of gases in liquids tends to increase with increasing pressure

Question 21

Solubility Rules for Salts

1. All Group I molecules: Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and ammonium (NH₄⁺) are soluble?/insoluble?
2. All nitrate, perchlorate, and acetate salts are soluble?/insoluble?
3. All silver, lead, and mercury salts are soluble?/insoluble?

Answer 21

1. All Group I molecules: Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and ammonium (NH₄⁺) are soluble
2. All nitrate NO₃^-, perchlorate ClO₄^-, and acetate C₂H₃O₂^- salts are soluble
3. All silver (Ag), lead (Pb²⁺/Pb⁴⁺), and mercury (Hg₂²⁺/Hg²⁺) salts are _insoluble *except when joined to nitrates, perchlorate, or acetates (from ^)_

Question 22

K_sp is?

Answer 22

solubility constant: the extent to which a salt will dissolve in water. It is just like any other K constant only the reactants and products are just undissolved and dissolved salts. (all other rules for K expression are the same):

^{1. no solids or pure liquids and}

^{2. the coefficient becomes the exponent}

Question 23

“ion product” refers to

Answer 23

the reaction quotient for a solubility reaction (meaning, it’s Q_sp)

*same rules for Q and K apply but it’s in terms of salt:

1. Q_sp < K_sp favors products, more salt dissolves
2. Q_sp = K_sp solution is saturated
3. Q_sp > K_sp favors reactants, more salt precipitates

Question 24

what is the relationship between ΔG , Q and K_eq ?

Answer 24

First of all, note that there has to be a relationship because ΔG=0 is essentially equilibrium, and ΔG changes before this point is reached. *ΔG° has a fixed relationship with K_eq for a given reaction.

The equation that relates it is

ΔG=ΔG°+RTlnQ

ΔG°= gibbs free energy for a reaction under standard conditions.

For an equilibrium equation, the above ^simplifies to

ΔG°=-RTlnK_eq

we get this by making ΔG =0 and saying Q is Keq at equilibrium

Question 25

T/F: ΔG° and K_eq have inverted relationships when not at equilibrium:

Answer 25

True:

favors products: ΔG° <0 and K_eq >1

favors reactants: ΔG° >0 and K_eq <1

equilibrium: ΔG° =0 and K_eq =1

Question 26

half-equivalence point vs equivalence point ?

Answer 26

half-equivalence point: the point at which half of the acid has dissociated (H-A=A^-)

pKa=pH of acid -aka isoelectric point around which is the buffering region

equivalence point: the point at which all of the original acid or base has been neutralized upon continual addition of base (for a monoprotic acid). It is the point between curves for a polyprotic acid

Question 27

how do you find the pH of a solution?

Answer 27

pH= pKa + log A^-/HA

where A^-/HA is in moles

Question 28

Answer 28

*if the concentration of A to HA is not in the same liter amount then the molarity is not the same and has to be converted first

Question 29

the K_a of HSCN is equal to 1 x 10^-4. The pH of a HSCN solution

1. can be known from the info given
2. cannot be known from the info given

Answer 29

cannot be known from the info given

we would have to know the concentration of hydrogen atoms or of the ratio of products to reactants

Question 30

special logs:

log 10 = ?

log 1 = ?

Answer 30

log 10 = 1

log 1 = 0

Question 31

the higher the pK_B the _______the base.

Answer 31

The equilibrium constant for a weak base is called K_B and the equation for K_B is: K_B = [BH+][OH] /[B] We can also convert between the pK_B and the K_B of a base, we only need to use the following equations: pK_B = -log(K_B)

High K_B means a “strong” weak base.

Low K_B means a “weak” weak base.

High pK_B means a “weak” weak base.

Low pK_B means a “strong” weak base.

Question 32

how does the pKa >/=/< pH relationship relate to the A- >/=/< HA?

Answer 32

pKa < pH → HA < A^- (more deprotonated species)

pKa = pH → A^-=HA

pKa > pH → HA > A^- (more protonated species)

_{<strong>mnemonic:</strong>}

_{everything on one side of the > signs match in terms of having the greater or lesser number of letters. for example,}

_{pKa has 3 letters and HA has 2 letters.. these are ALWAYS on the same side in relationship to > sign and visa versa}

Question 33

↑pKa ↑?↓? pH

Answer 33

↑pKa ↓pH

Question 34

amphoteric refers to

Answer 34

able to react both as a base and as an acid.

e.g.

Question 35

proton dissociation increases/decreases/neither the K_w?

Answer 35

neither! nothing but temperature changes any K value

Question 36

in a litmus paper test, what color indicates basic and what color indicates acidic?

Answer 36

yellow litmus paper: blue is basic and red is acidic, with the range corresponding to ROYBIV.

blue litmus paper:

basic → stays same

acidic→ turns red

red litmus paper:

basic → turns blue

acidic → stays same

Question 37

solve

Answer 37

C turn blue because it reacts with water to form OH-

Question 38

what does this notation indicate and what do you do with it mathematically?

Answer 38

it means hydration. the 6 number indicates the max number of water molecules that can be incorporated into the chrystaline structure of the compound during solvation.

mathematically, just treat them both like reactants. the MW was compute from simply addition (NOT multiplication)

Question 39

How many moles of Ni in a 7 g sample of NiSO₄ •6H₂0 (MW 262.84) dissolved in enough water to make 50mL of a solution.

^how do you solve this?

Answer 39

Answer: 6/262.84 = 0.025

(the number of liters doesn’t effect number of moles)

my instinct is to always try to divide the weight by the molecular weight of just the atom I’m trying to find (e.g. 6.57/58 for nickel) But that is WRONG.

6/262.84 gives you the number of moles of the entire molecule OR the number of moles of each individual component of NiSO₄ because moles is just the number of them that exists and whether they are separate or apart, they exist in units of moles.

analogy: If I’m walking with sean we are a couple and there is 1 of us, but if I am walking by myself I am not a couple but there is still 1 of me. either way there’s 1 (where 1 would be the number of moles in this scenario)

Question 40

CO₃^2- will react with a proton source (HCl) to form ?

Answer 40

CO₂ and OH^-

Question 41

T/F: bases can be identified from the fact that they will dissociate -OH in an aqueous solution

Answer 41

True,

so OH will be in their chemical formula

Question 42

the Heisenburg uncertainty principle dictates that as you decrease the uncertainty of the position you increase the certainty of

Answer 42

momentum

*and visa versa