Advanced higher chemistry unit 2

chemical reaction in equilibrium

when compositions of reactants and products remain constant indefinitely

general reaction and equation for equilibrium constant ( K ) for equilibrium composition of general reaction

what does value of equilibrium indicate and effect of pressure or concentration

position of equilibrium

equilibrium constants are independent of the concentration or pressure of species in a given reaction

numerical value of equilibrium constant depends on what

reaction temperature

for endothermic reactions a rise in temperature causes an increase in K so yield of the product is increased

for exothermic reactions rise in temperature causes decrease in K so yield of the product is decreased

the presence of catalyst dosent affect equilibrium constant value

what occurs between water and aqueous solutions

there is equilibrium between water molecule and hydronium ( hydrogen ) and hydroxide ions

hydronium ion/hydrated proton = H3O+ (aq) or H+ (aq)

water is amphoteric react as acid and base

equation ionisation of water

dissociation constant for ionisation of water

ionic products Kw

value of ionic product at room temperature

Kw is 1 × 10^-14

relationship between pH and hydrogen ion concentration

water and aqueous solutions pH 7 concentration of H3O and OH are what

10^-7 at room temp

how concentration of other ion calculated if OH or H3O is known

using Kw or using pH + pOH = 14

bronstead definition of acid and base

acid is proton donor

base is proton acceptor

conjugate acid and base

for every acid there is a conjugate base formed by loss of proton

for every base there is conjugate acid formed by gain of proton

strong and weak acid and bases

strong acid and bases are completely dissociated into ions in aqueous solution

weak acid and base only partially dissociated into ions in aqueous solutions

example of strong and weak acid and base

strong acid/ base - hydrochloric sulfuric nitric metal hydroxide

weak acid/base - ethanoic carbonic sulfurous ammonia amine

equation for acid dissociation constant ( Ka)

Ph of weak acid equation

salts produced by weak or strong acid and base

soluble salt of strong acid strong base dissolves in water to produce neutral solution

soluble salt of weak acid strong base dissolve in water to produce alkanline solution

soluble salt of strong acid weak base dissolve in water to form acidic solution

buffer solution

pH remains approximately constant when small amounts of acid base or water is added

acid buffer

solution of weak acid and one of its salts made from strong base

weak acid provides hydrogen ion when these are removed by addition of small amount of base

salt of weak acid provides conjugate base which can absorb excess hydrogen ions produced by addition of small amount of acid

basic buffer

solution of weak base and one of its salts

solution of weak base removes excess hydrogen ions and the conjugate acid provided by salt supplies hydrogen ions when these are removed

pH of acid buffer calculation from composition from acid dissociation constant

weak acid or indicator dissociation and equation

Hin ( AQ ) + H2O (L) - H3O+ (AQ) + Ln^- (AQ)

indicators ( weak acid )

in aqueous solutions colour of acid indictaor is distinctly different from that of its conjugate base

colour indicator determined by ratio of (Hln) to (In-)

theorterical point at which colour change is when (H+)=KIn

colour change is assumed to be distinguishable when (HIn) and (In-) differ by factor of 10

pH range over which colour change occurs estimated by expression pH= pKIn ± 1

standard enthalpy of formation triangleHf and equation

enthalpy change is when one mole of substance is formed from its elements in their standard states

standard state of substance is its most stable state at the pressure of 1 atmosphere and specified temperature usually 298 K

entropy ( S )

measure of degree of disorder of the system

greater degree of disorder the greater the entropy

solids have low degree of disorder gases have high disorder

entropy increase as temp increase

rapid increase of entropy at melting point of substance and an even more rapid and larger change in entropy at boiling point

second and third law of thermodynamics ( equation of standard change entropy )

2nd law states total entropy of reaction system and its surrounding always increases for spontaneous process

heat energy released by reaction system into surroundings increases entropy of surroundings whereas heat absorbed by reaction system from surroundings decreases entropy of surroundings

third law states entropy of perfect crystal at 0k is 0

standard entropy of substance is entropy value for substance in standrad state

change in free energy

if change in free energy is negative a reaction may occur and reaction is feasible

feasible reaction is one tends towards products rather than reactants dosent give any indication of rate of reaction

Standard free energy change for reaction

what happens at equilibrium at deltaG=0

reaction will proceed spontaneously in forward direction until the composition is reached where deltaG=0

orders of reaction and summary of units

rate of reaction normally depends on concentrations of reactants

used to relate rate to reacting species

0= mol l -1 s -1

1= s-1

2= mol-1 l s-1

3= mol-2 l-2 s-1

reaction mechanisms

reactions usually occur by series of steps called reaction mechanism

rate dependent on slowest step called rate determining step

experimentally determined rate equation provide evidence for proposed reaction mechanism