equilibrium + acids/bases Flashcards
chemical kinetics
the study of reaction rates
collision theory
for a reaction to occur, substance particles must physically collide in space
effective collisions
- a collision must be effective for a rxn to occur
- the molecules must collide in the correct orientation, and with sufficient energy
activation energy
the minimum energy required for a reaction to occur
transition state
- when bonds are broken, produces an unstable, temporary molecule
“activated complex” - as rxn continues, will settle into product
catalyst
a substance that reduces the activation energy of a reaction by changing reaction pathway without being consumed so that the transition state is different and lower in energy
rate of reaction
how fast a reaction progresses & proportional to the number of effective collisions per second
increase reaction rate by:
-more reactant surface area
-higher temperature
-a catalyst
-increasing concentration
surface area (rxn rate)
more surface area btw reactants=more collisions=more effective collisions=higher rxn rate
dissolving into solutions gets maxium surface area (liquids & gases)
temperature (rxn rate)
increase in temperature means an increase in kinetic E of the reactants=more reactants able to overcome the activtion E=higher rxn rate
concentration (rxn rate)
higher concentration of reactants=more collisions=more effective collisions=higher rxn rate
as a rxn progresses, reactants turn to products so concentration drops & rxn rate slows over time
pressure for gaseous systems (rxn rate)
increase in pressure=more particle-wall collisions=more particle-particle collisions=more effective collisions=higher rxn rate
as a rxn progresses, reactants turn to products so reactant pressure drops & rxn rate slows over time
catalyst (rxn rate)
adding a catalyst lowers the activation energy so more particles can overcome the activation barrier, and increases rxn rate
activation energy & rxn rates
higher activation energy (less collisions with enough energy to overcome the barrier) means slower rate & vice versa
reversible reactions
when the energies of the reactants & products are similar, no matter the amount of activation E, the rxn rates are similar & the reaction is reversible
irreversible reactions
if the energies of the reactants & products are different, the activation E of one will be a lot larger & the reaction will be irreversible
reaction rates in action
- forward reaction rates are higher when there’s more reactants
- reverse reaction rates are higher when there’s more product
- as one dwindles the other will become more of
- rates (not necessarily concentration of matter) will become equal at equilibrium
chemical equilibrium
when the rate of the forward reaction & the rate of the reverse direction are equal (not zero); reactants and products are still doing their reactions it’s just that there’s no net change
closed systems
to reach equilibrium, reactions must take place in a closed system where no matter can be exchanged with its surroundings (energy is fine)
Keq
a state of equlibrium: a ratio of products to reactants once a stable equilibrium is reached (@ a standard temperature)
Kc
a molarity Keq; pure solids & liquids not included, only for gaseous & aqeous reactions
the concentration of products raised to the power of their coefficients over the concentration of reactants raised to the power of their coefficients
Kp
only for gaseous reactions, a partial pressure Keq
the partial pressure of products raised to the power of their coefficients over the partial pressure of reactants raised to the power of their coefficients
temperature dependance
an equilibrium constant is specific for a certain temperature as the ratio of reactants and products change when temperature fluctuates
reaction quotient
Q is the ratio of reactant to product concentration at any other time but equlibrium (basically Kc but not at equlibrium)
Q<K
reaction goes to the right, and more product is created
Q>K
reaction goes to the left, and more reactant is created
Q=K
reactant is at equilibrium, and nothing will change
Q or Keq in the reverse direction
Q or Keq in the reverse direction is the inverse of it in the forward direction
equilibrium calculations
use an ICE chart to calculate concentrations at equilbirum when given inital amounts of reactant or products
equilibrium approximations
when the equilibrium constant is very small, we can approximate
[initial] - x ≈ [initial]
approximation can be made when there are at least four orders of magnitude between the equilibrium constant & initial concentration
arrhenius acids&bases
arrhenius acids produce H+ ions (H3O+) when dissolved in water
arrhenius bases produce OH- ions when dissolved in water
le chatelier’s principle
when a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance (in order to return to an equilibrium state)
changing concentration
adding more of an aqueous or gas reactant or product shifts the equilibrium away from that species to use enough –> equilibrium
- add more product, Q increases
- add more reactant, Q decreases
adding pure solids/liquids to equilibrium
no effect: pure solids & liquids are not included in the equilibrium constant
exothermic direction
direction that goes from higher energy to lower energy: produces heat
endothermic reaction
direction that goes from lower energy products to higher: requires heat
changing temperature
increasing the temperature will shift the reaction such that it absorbs heat (towards endothermic direction)
decreasing the temperature will shift the reaction such that it produces heat (towards exothermic direction)
changing pressure: volume
changing the volume will change not only total but also partial pressures:
increasing volume decreases partial pressures & the reaction will shift to the side with more moles of gas, helping to offset the overall pressure decrease (resisting a vacuum)
decreasing volume increases partial pressures & the reaction will shift to the side with fewer moles of gas, helping to offset the overall pressure increase
changing pressure: adding inert gas
inert gas: noble gas
adding an inert gas increases the overall pressure of the system, but not the partial pressures –> no change in equilibrium
adding a catalyst
no change to equilibrium: increases rxn rate of both directions
bronsted-lowry definitions
-a Brønsted-Lowry acid is a proton donor
-a Brønsted-Lowry base is a proton acceptor
-acid/base reactions are therefore a proton transfer, by definition, from an acid to a base
autoionization of water
water molecules constantly self dissociate, with one water molecule being the bronsted-lowry base and the other the acid
the specific equilibrium constant for this is Kw
Kw
[H30+][OH-] = 1x10^-14
in a neutral solution, the concentration of the 2 must be equal –> each is 1x10^-7M
as one increases, the other must decrease
hydrolysis in acids/bases
hydrolysis in acid: water acts as a base & accepts the proton
HA(aq) + H2O(l) ⇋ H3O+(aq) + A-(aq)
hydrolysis in base: water acts as an acid & donates a proton
B(aq) + H2O(l) ⇋ BH+(aq) + OH-(aq)
acidic vs. basic solutions
- if H30 ion concentration is > 1x10^-7 M, acidic
- if H30 ion concentration is < 1x10^-7, basic
pH & pOH
pH = -log10 [H30]; [H30]=10^-pH
pOH = -log10 [OH]; [OH]=10^-pOH
-logKw = pH + pOH = 14
strong acids
HCl, HBr, HI, HClO3, HClO4, HNO3, H2SO4
any of above + H20 – H3O + conjugate base
for weak acids, reaction is reversible & in equilibrium
strong bases
group 1/2 hydroxides
MOH + H20 – conjugate acid + OH
for weak bases, reaction is reversible & in equlibrium
Ka
the Kc for weak acids
HA + H2O – A- + H3O+
the larger Ka is, the stronger the acid is/more it dissociates
pKa
is just -log(10) Ka
neutralization reaction
a reaction between acids and bases forming water and a salt (ionic compound)
If the base does not contain hydroxide (weak base), water will not be a product
HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)
equivalence point
(in a neutralization rxn) a point where moles of the acid=moles of the base
strong acid/strong base
irreversible, find pH from [excess reagent]
if both H3O & OH are at the equivalence point, they will both be consumed & reactoin will be netural
pH can be determined from the concentration of excess reagent
weak acid/strong base
strong acid/weak base
it will go to completion, if the excess is weak, then find the concentration using Keq; if the excess is strong, ah fuck it alllll
