chem 2 exam 1

Final energy of products is lower than reactants

reaction is exothermic, ΔHrxn = negative, releases heat

Final energy of products is greater than reactants

endothermic, Δrxn = positive, need heat to make reaction go

Activation energy

energy that must be overcome for reaction to proceed

always positive (if not gained by reaction, reaction can’t proceed)

catalysts lower activation energy (increases reaction rate without being consumed) (also speeds up forward and reverse reactions and doesn’t affect ΔH or overall yield for a reaction)

Transition state

enough energy is gained by reaction where old bonds are broken and new bonds form (converting reactants to products)

peak of hump → number of transition states (humps), number of steps in reaction

Activation energy is

not dependent on the temperature, but rate constant does depend on temperature

Arrhenius Equation

single rate: A * e^-Ea/RT

Equilibrium

state where forward and reverse reactions continue to occur at equal rates so no net change is observed once equilibrium is reached.

constant k

k

always greater than 0

if large (k>1) reaction is product favored, lies to the right

if small (k<1) reaction is reactant favored, lies to left

doesn’t tell us which way to shift - Q does (k is the number we’re trying to get to)

Reaction shifts

Q < k (reac → prod) shift right

Q = k (equili) no shift

Q > k (reac ← prod) shift left

Partial Pressure of A

P_A=X_A * P_Total

Kp and Kc

EQ→ 1. Balanced, 2. K’s match, 3. Same Temp

Δn= total moles of gas products - total moles of gas reactants

Le chatelier’s principle

1. change that disrupts EQ, 2. a shift that brings it back to EQ

temperature

exothermic ΔH in product (negative)

endothermic ΔH in reactant (positive)

• temp is only factor that changes actual value of k

• if you change temp and shift right, k increases

• if you change temp and shift left, k decreases

pressure

affects the side of reaction with most mols of gas (volume is opposite) (not same as partial pressure)

at equili, addition of a catalyst

has no effect on shift of the reaction

adding an inert gas (noble gas)

• at constant volume doesn’t affect equili (since pressures are allowed to change)

• at constant pressure, pressures of the components will decrease so it will shift EQ toward more moles of gas

endo

exo

• incr temp, incr k

• incr temp, decr k

arrhenius acid

arrhenius base

substance with H in formula that dissociates in water to yield H3O+

subatnce with OH in formula that dissociates in water to yield OH-

• reactions between acid and base are nuetralization reactions (produce H2O)

• strength of acid/base depends on how much H+ or OH- it releases into water (stronger they are, the more it dissociates and releases these)

strong electrolytes

strong acid, strong base, soluble salet - all dissociate completely in solution

weak electrolytes

weak acid, weak base, insoluble salt - do not dissociate completely in solution- more like 10%

bronsted-lowry acid

bronsted lowry base

species that gives up H+ to H2O (proton donor) (+ or H+)

• Monoprotic acid: can donate only one proton

• Polyprotic acid: can donate more than one proton.

species that accepts H+ from H2O (proton acceptor) (- or lone pair)

• monoprotic base: can accept only one proton

• polyprotic base: can accept more than one proton

amphoteric substances

capable of accepting a proton or donating a protom ex: HCO3- or H2O

conjugate acid-base pair

pair of compounds or ions that differ by presence of one H+ ion

• bronsted-lowry acid produces conjugate base (CB)

• bronsted-lowry base produces conjugate acid (CA)

NxHy

base (weak if no charge) except NH2- = SB

auto-ionization

water ionizes to create hydronium and hydroxide - this gives water its duality to become acid/basic in solution

H2O + H2O → H3O+ + OH-

concentrations

H3O = OH , neutral, pH and pOH = 7

H3O > OH, acidic, pH < 7, pOH > 7

H3O < OH, basic, pH > 7, pOH <7

pH

measure of hydronium ion concentration

-log[H3O] = pH

[H30] = 10^-pH

pOH

measure of hydroxide ion concentration

-log[OH] = pOH

[OH] = 10^-pOH

pH + pOH =

pKw

at 25°C pKw = 14.00

Kw = [H3O+][OH-] at 25°C, Kw = 1.0 ×10^-14

(number of decimal places in pH/pOH = # of sig figs in concentration)

increase temp, increase k

pH changes

Strong acids (SA)

produce H3O+ and the conjugate base ex: HCl and HNO3 (with H2O in equation?)

(for C of ICE since it’s strong don’t use x use the concentration given)

Strong Bases (SB)

produce OH- and the counter ion ex: OH- and NH2-

(for C of ICE since it’s strong don’t use x use the concentration given)

the larger the Ka

the larger the Kb

the stronger the acid, if Ka > 1, substance is strong acid

the stronger the base, if Kb > 1, substance is a strong base

Ka (acid) * Kb (its conjugate base) = Kw (1.0 ×10^-14 at 25°C

Ka reactions

Kb reactions

when acids react with water

when base reacts with water

pKa + pKb =

pKw

pKa = -logKa, as pKa decreases, the strength of the acid increases

pKb = -logKb, as pKb decreases the strength of the base increases

conjugate theory

if strong acid, its conjugate base has no basic properties

if strong base, its conjugate acid has no acidic properties

(as acid strength increases the conjugate base strength decreases) (the stronger the acid the weaker its conjugate)

lower pH =

higher pH =

stronger A (stronger acid, weaker base)

stronger B

if stronger acid/base is on left side

equili lies to right (product favored)

Kc >1

if stronger acid/base is on right side

equili lies to left (reactant favored)

Kc < 1

higher [H3O+] =

higher [OH-]

more acidic

more basic

(also stronger acid should have lower pH)

weak acids remain in solution and

weak bases remain in solution and

don’t produce much H3O+

don’t produce much OH-

approximation assumption to solve for x

[HA]i / Ka > 400

% ionization

amount of substance that is lost/gained by the reactant/product in an equili reaction to reestablish equili

amount lost (x)/ Mi * 100%

approx is okay if it’s less than 5%

polyprotic acids

acids that contain two or more ionizable protons

ionize in successive steps - lose H+ one at a time (with each H+ lost having a Ka)

acid ionization constants get smaller and smaller: Ka1 > Ka2 > Ka3

• determine pH of a weak polyprotic acid: only must use the first dissociation of acid

• second dissociation always equal k2 if weak acid/base

Neutral ions

conjugate bases of most strong acids

• Cl-, Br-, I-, ClO4-, NO3-

Group 1A and 2A metal cations

• Li+, Na+, Ca2+, Sr2+, etc.

Acidic Ions

conjugate acids of weak bases

• NH4+, C5H6N+

Highly charge-dense metal cations

• Al3+, Fe3+, transitions

HSO4-

basic ions

conjugate bases of weak acids

• F-, SO4²-, CN-

acidic ion and basic ion

if Ka for acid is > Kb for base, solution is acidic.

if Kb for base is > Ka for acid, solution is basic.

if Ka for acid = Kb for base, solution is neutral

nonmetal hydroxides (HX)

one or more hydrogen atoms covalently bonded to a nonmetal

down a group, HX acid strength increases (bc of increase in size of anion, larger anion leads to a weaker bond)

left to right across period, HX acid strength increases (bc of increase in EN of nonmetal, more EN element leads to more polar bond→ more acidic easier to leave)

hydrated metal cation

highly charge-dense central ion with water molecules attached via coordinate-covalent bonds

larger the charge, higher the acidity . if charges are same, smaller the cation, the higher the acidity

exceptions: transition metals tend to have higher acidity than representative metals

oxoacids

acids that contain at least one oxygen atom in their compound

• diff number if oxygen atoms → more oxygen atoms = more acidic acid. more oxygen atoms means a higher oxidation state for the nonmetal resulting in a more polar O-H bond.

• same number of oxygen atoms → more EN = more acidic

only way to know which acid is stronger for sure is compare Ka’s (only use these trends if not given Ka value)

Lewis acid

lewis base

substance that can accept a pair of electrons from another atom to form a new bond (Cr3+, Ni2+, SF4, BeCl2, CO2)

substance that can donate a pair of electrons to another atom to from a new bond (NH3, CH3NH2, F-, H2O → but water not always a LB)

levelling effect

when a strong acid or strong base is added to water, they will level off to form H3O or OH (like HCl, HNO3, and CaO, Na2S, NaOH)