Chemical Equilibrium Flashcards
concentration value of solid or solvent in equlibrium constant equation
1
effect of catalyst on equilibrium constant and position
no effect, equilibrium is just reached faster
effect of temperature change on equilibrium constant and position
if temp increased, endo reaction favoured
if temp decreased, exo reaction favoured
(if moved to left, K will decrease)
K
equilibrium constant
equilibrium in water and aqueous solutions
equilibrium between water molecules and hydrogen and hydroxide molecules
H2O(l) + H2O(l) H3O+(aq) + OH-(aq)
H30+ (aq)
same as H+, hydronium ion
Kw
dissociation constant of water, value of ionic product varies with temp
value of Kw at 25oC
1.0 x 10-14
amphoteric and example
can act as an acid and a base, depending on environment, ex. water, aluminium oxide
strong acid
completely dissociates in aqueous solution, regardless of concentration eg. nitric, hydrochloric
weak acid
partially dissociates in aqueous solution eg. methanoic, carbonic
equilibrium postion in weak acid dissociations
well to the left, very little H+ ions in acid solution
bases
substances that can reaction with H+ to form water
strong base
ionic and dissociate completely, ex. metal hydroxides
weak base
partially dissociate, ex. ammonia and amines
strong base pH and conductivity
high pH (13-14) and conductivity
weak base pH and conductivity
low pH (11-12) and conductivity
salts of a weak acid and strong base give
alkaline solution
salts of strong acid and weak base give
acidic solution
salts of strong acid and stong base give
neutral solution
stoichemistry
numerical propotions of substances involved in a reaction
concentrations of H+ and OH- in water at 25C
10^-7 mol
bronsted- lowry defintion of acids and bases
acids= proton donators
bases= proton acceptors
conjugate base and acid= formed by acceptance and donation of protons
proton
H+ ion
buffer
solution in which pH stays approximately constant when small amounts of acid or base are added
what are buffers made from?
weak acid and one of its salts or weak base and one of its salts
how does a buffer work if acid is added?
introduced ions combine with A- ions from salt to form HA, H+ ions are mopped up so no fall in pH
how does a buffer work if a base is added?
OH- and H+ react to form water but equlibium shifts to regenerate more H+ ions so no fall in pH
pH of buffer solution equation
pH= pKa - log [acid]/[salt]
[ ]
concentration
acid indicator dissociation constant equation
Kin= [H+][In]/[HIn]
equivalence point
theoretical point at which colour change occurs, H+= KIn
what are indictors usually made of?
weak acids which the colour of the base is different to the colour of it’s conjugate base
enthalpy of formation
enthalpy change when one mole of a substance is formed from elements in standard states
standard conditions
298K (25C) and one atmosphere
entropy of a system
measure of disorder of system, greater disorder= greater entropy, change in state involves changes in entropy
entropy when solid reactants change to gaseous products
postive
second law of thermodynamics
total entropy of a reaction system and its surroundings always increase for a spontaneous reaction, heat energy released by reaction system increase entropy of surroundings and heat energy absorbed decreases entropy of surroundings
entropy of a perfect crystal at 0K
0
what is the standard entropy of a substance?
entropy for the standard state of a substance
spontaneous reaction
can occur on its own
if ΔS>0 is reaction spontaneous?
postive entropy change, reaction is spontaneous
if ΔS<0 is reaction spontaneous?
negative entropy change, reaction is not spontaneous
ΔG
free energy
if there is a negative change in ΔG, is the reaction spontaneous?
yes, equilibrium composition favours products over reactants
equation for change in free energy
ΔG= TΔS
entropy units
JK-1
equation to find what temperature a reaction becomes feasible
T= ΔH/ΔS
rate equation
rate= k[A][B]
k
rate constant
if rate doubles when [A} doubles and quadruples when [B] doubles…
reaction is first order with regards to A anf second order with regards to B
if doubling [A] doesnt affect rate of reaction what order is it?
zero order
what can order of a reaction only be determined from?
experimental data
if overall order is 0 what are the units for k?
mol l-1 s-1
if overall order is 1 what are the units for k?
s-1
if overall order is 2 what are the units for k?
mol-1 l s-1
if overall order is 3 what are the units for k?
mol-2 l2 s-1
rate constant equation
k= rate/[A][B]
rate determining step
slowest step in reaction mechanism which the rate of reaction is dependant on
