KINETICS Flashcards
units for rate of reaction
mol dm^-3 s^-1
why must total volume be kept constant
so that the initial conc of each rxtant in the rxnt mixt will be directly proportional to its volume used
how does addition of catalyst affect rate
Ea decreases, k increases, rate increases
k formula(3)
k=Ae^-Ea/RT
k=ln2/t1/2(normal rxn)
k=ln2/t1/2[XS/catalyst] (pseudo or catalyst rxn)
k=rate/[reactants]
effect of catalyst on rate of rxn with diagram
-catalyst provides an alternative pathway of lower activation energy
The addition of catalyst lowers Ea from Ea(uncat) to Ea(cat), the no. of reacting particles w/ energy more than or equals to Ea increases, frequency of effective collisions per unit time in the rxn increases, since rate of rxn is proportional to freq of eff coll, rate of rxn increases
factors affecting rate of rxn
conc of rxtant, catalyst, temp, SA
effect of temp on rate of rxn w maxwell boltzmann diagram
When temp of rxn increases, avg KE of rxtant particles increases, there are more reactant particles with energy more than or equals to Ea, frequency of effective collisions increases, rate of rxn increases
how does adsorption work for heterogenous catalyst
1) rxtant molecules diffuse towards solid cat surface and is adsorbed at active sites at surface
2)adsorption increases conc of rxtant molecules on catalyst surface
3) intramolecular bonds within rxtant molcules are weakened, lowering Ea
4) pdt molecules desorbs and diffuses away from catalyst surface
properties of enzymatic catalyst
remains chemically unchanged at end of rxn, required in small qty, denatures at high temp(heat energy overcomes bonds that hold structure tgt, resulting in shape of active sites lost)
effect of low conc of substrate on rate of reaction(enzymatic catalyst) OR
explain r/s b/w [substrate] and rate of enzyme catalysed rxn
-active sites of the enzymes are not fully filled
-rate of rxn follows 1st order wrt substrate, where rate is directly prop to [substrate]
-rate of rxn increases
effect of moderate conc of substrate on rate of reaction(enzymatic catalyst) OR
explain r/s b/w [substrate] and rate of enzyme catalysed rxn
-less significant increase of graph in the middle
-rxn is mixed order wrt intermediate substrate
-rate of rxn increases to a lesser extent
effect of high conc of substrate on rate of reaction(enzymatic catalyst) OR
explain r/s b/w [substrate] and rate of enzyme catalysed rxn
-all active sites are fully saturated
-any increase in [substrate ]no longer increases rate of rxn as there are no longer any active sites avail for substrate to attach to and rxt with
-the reaction is zero order wrt substrate
defn of t1/2
the time taken for the conc of rxtant to reduce to 1/2 of its original conc
effect of SA of rate of rxn
the more finely divided solid, the larger the surface area, frequency of effective collisions b/w rxtant p increases, rate of rxn increases
effect of conc of rxtant on rate of rxn
-conc of rxtant increases
-rxtant particles PER UNIT VOL increases
-freq of eff coll b/w rxtant particles increases, rate of rxn increases
effect of pressure on rate of rxn(only for gaseous rxn)
-pressure of gaseous rxn increases by reducing volume
-rxtant p are forced closer tgt in a smaller vol
-freq of eff coll b/w p increases
-rate of rxn increases
Comment if reaction is expected to occur via one elementary step(BrO3- +5Br- + 6H+)
No, it is extremely unlikely for so many(12) reactant species to collide at the appropriate geometry
1st order reactant formula
[A remaining]/A[initial] = (1/2)^(t/t1/2)
