4. Chemical Reactivity Flashcards
what does pressure favor for equilibrium
Favours form of fewer moles of gas
what is the equilibrium constant
conc of reactant and product at equilibrium
what is the unit for equilibrium constant
molL-1
what does a large kc >10^5 mean
completely convert reactant to product
what does a very small kc <10^-5 mean
very small number of reactants turn into products
what is the unit for solubility
gL-1
what is the reaction quotient
determines direction reaction shifts to reach equilibrium
what does it mean if Q<K for the reaction quotient
forwards/to the right
reactant to product
what does it mean if Q>K for the reaction quotient
reverse/to left
products to reactants
precipitation
what does it mean if Q=K for the reaction quotient
reaction is already at equilibrium
what is Q regarding the reaciton quotient
ionic product
what does increased conc of the ion or common ion effect do to the reaction in terms of direction itll proceed and solubility
drives reverse reaction
decrease solubility
what is the common ion effect
add reagent with which cations form soluble complex
eg Ag+ + 2NH3 -> [Ag(NH3)2]+
what is the colour of phenolphthalein in acid and base
acid = colourless
base = pink
what is the colour of bromothymol blue in acid and base
acid = yellow
base = blue
what does acids do in terms of protons
transfer/donate H+ to others
what does bases do in terms of protons
accept H+ from others
increase conjugate acid strength does what to the base strength
decreases conjugate base strength and vice versa
what is ka’s relationship with acid strength
increased ka = stronger acid
what is ka’s relationship with pka
increase ka = decrease pka
what is pka’s relationship with acid strength
small pka = stronger acid
what is the equation relating pka and ka
pka = -log10ka
ka = 10^-pka
if the buffer is equimolar then what is the relationship of the pH of the buffer and the pka of acid
pH buffer = pka acid
for a titration of weak acid/base and added strong acid/base how do you calculate the pH of the original acid
added volume of strong base/acid = 0 at this point
- write reaction equation for the weak acid/base
- write ka expression
- solve for [H3O+]
for a titration of weak acid/base and added strong acid/base how do you calculate the volume of added acid/base at equivalence
equivalence point = n(acid) = n(base)
- find n(weak acid/base)
- mole ratio of weak acid/base and added volume
- find n(added volume) from ratio mole
- find volume thats added via C=n/V
for a titration of weak acid/base and added strong acid/base how do you calculate the volume of added acid/base when pH = pka
pka = pH when v(added volume) = 1/2 amount of weak acid/base
v(added) = v(equivalence)/2
for a titration of weak acid/base and added strong acid/base how do you calculate pH
- write equation for reaction between weak acid/base with added strong acid/base
- identify ka or kb expression
- find [ion react with H2O] via C=n/V
- solve ka or kb for [H3O+]
for a titration of weak acid/base and added strong acid/base how do you calculate the pH after x amount of added volume is added
after equivalence will have extra of added volume
- new conc = original conc x (extra volume/total volume)
- find [H+] to find pH
what is the buffer zone
where buffer is effective over pH range of pka +/- 1
for a zero order reaction what is the change in rate when there is a change in [A]
what equation represents this - rate is proportional to.. and rate = …
no change in change in rate
rate proportional to [A]^0
rate = k
for a first order reaction what is the change in rate when there is a change in [A]
what equation represents this - rate is proportional to.. and rate = …
rate x2 when [A] x 2
rate proportional to [A]^1
rate = k[A[
for a second order reaction what is the change in rate when there is a change in [A]
what equation represents this - rate is proportional to.. and rate = …
4 x rate when [A] x 2
rate proportional to [A]^2
rate = k[A]^2
for a zero order reaction what is the unit of k
molL^-1s^-1
for a first order reaction what is the unit of k
s^-1
for a second order reaction what is the unit of k
Lmol^-1s^-1
for a third order reaction what is the unit of k
L^2mol^-2s^-1
what is the [R] rate law equation for first order reaction
[R] = [Ro]e^(-kt)
ln[R] = ln[Ro] - kt
for a first order reaction what is the plot of ln[R] vs time like
linear
what are the 2 possible combinations of 2nd order reaction
single reactant in 2nd order
or
2 reactants in first order
what assumption is made for a second order reaction that is made up of 2 1st order reactions
that one of the reactants’s conc is very large
what is the rate law equation for second order reaction and a pseudo first order
1/[R] = 1/[Ro] + kt
k1 = [R]
pseudo first order
what is the half life rate equation for zero order reactions
[R] = [Ro] - kt
t1/2 = [Ro]/2k
what is the half life rate equation for first order reactions
ln[R] = ln[Ro] - kt
t1/2 = ln2/k
what is the half life rate equation for second order reactions
1/[R] = 1/[Ro] + kt
t1/2 = 1/[Ro]k
what is the half life
time for conc of reactant to fall to 1/2 its original value
what are the 2 conditions for a effective collision
molecule has high enough energy to overcome activation energy
correctly aligned molecules
what is the relative energy of the multistep reactivity when it comes to reactive intermediates
minimum energy
what is the relative energy of the multistep reactivity when it comes to transition states
max energy
when do catalysts act in the reaction pathway
usually early step and regenerates in later step
what are homogenous catalysts
catalysts working in same phase as reaction
what are heterogenous catalysts
catalysts working in different phase from reaction
what do catalysts do - 2 possible actions
provides different path of lower Ea = faster reaction rate
or
molecules are aligned by the catalyst
what is the rate determining step
the slowest step
what are bronstead acids
proton H+ can be taken by base
what are bronstead bases
take proton H+ from acid
what are amphoteric substances
can act as both acid or base
what does a -pH mean
pH is + for [H+] <1molL^-1
-pH means very acidic
what are the bonds like in strong acids
what does this mean for the distance between atoms and the e- density
short bonds so atoms are closer together
e- density between 2 atoms is large
decrease in e- density of bond means what for the strength of the bond
decrease strength of bond
what are the 2 ways that the e- density in bond regarding acidity of substance be affected
decrease amount of charge
charge stabilization
why does decreasing the amount of charge affect the e- density in bond regarding acidity of substance
easier for + molecule to lose + H+ ion so if acid loses H+ then the conj base is 1 unit charge more negative
what are the 2 ways that charge stabilization affect the e- density in bond regarding acidity of substance
- inductive effects
- delocalisation
for charge stabilization affecting the e- density in bond regarding acidity of substance - explain the inductive effects
presence of nearby electronegative atom/e- withdrawing groups move charge away from acidic H = weaker H bond
for charge stabilization affecting the e- density in bond regarding acidity of substance - explain the delocalisation effects
spread charge over larger number of atoms - occurs via resonance
regarding speciation
if pH < pka what does this mean for the acid and base forms
have higher acid forms (HA) than base form proportionally
regarding speciation
if pH > pka what does this mean for the acid and base forms
have higher base forms (A-) than acid form proportionally
how do you calculate the pH of an amphoteric substance solution
pH = 1/2(pka1 + pka2)
buffers work best in what range
at pH = pka +/- 1