6. Kinetics

Question 1

Define rate

Answer 1

Change in concentration of reactants/products with time.

Question 2

Define rate equation

Answer 2

An experimentally determined equation that links the rate of reaction to the concentration of each reactant/catalyst raised to a specific power.

Question 3

Define order of reaction

Answer 3

Power to which the concentration of that reactant/catalyst is raised in the experimentally determined rate equation.

Question 4

Define rate constant

Answer 4

Proportionality constant.

Question 5

Define half-life

Answer 5

Time taken for concentration of reactant to reduce to 1/2 its initial value.

Question 6

Define rate-determining step

Answer 6

Slowest step in a reaction.

Question 7

Define catalyst

Answer 7

Substance that increases the rate of reaction by providing an alternative pathway with lower activation energy, without itself undergoing permanent chemical change.

Question 8

whats the eqn to find k or t½

Answer 8

k = ln2/t½

Question 9

why rate prop to time taken

Answer 9

rate = amt reactant/time
as fixed amt reactant, …

Question 10

why conc of reactant is prop to vol of reactant

Answer 10

conc mixture
= n/V.total
= conc.added x V.added / V.total
= k(V.added)
cuz conc.added / V.total is constant

Question 11

format for determining order of rxn

Answer 11

Comparing expt 1&2, when [A] inc __ times, rate inc __ times, order of rxn wrt A is __

Question 12

why fixed amt S2O3 2-

Answer 12

ensure amt of I2 prod when dark blue appears is constant

Question 13

why cannot large amt S2O3 2-

Answer 13

1. formation of dark blue takes longer time –> poor approx init rate
2. no dark blue colour formed as all I2 has been reduced to I-

Question 14

what happens when inc conc of reactants (diagram thing）

Answer 14

inc no of particles per unit vol –> inc freq effective collisions –> inc ratw of rxn

Question 15

what happens when inc temp (diagram thingy)

Answer 15

av KE inc –> more particles possess energy >= Ea –> inc freq effective collisions –> rate constant inc –> rate inc

Question 16

what happens when catalyst (diagram thingy)

Answer 16

provide an alt pathway w lower Ea –> more particles possess energy >= new Ea –> inc freq effective collisions –> rate constant inc –> rate inc

Question 17

adsorption theory

Answer 17

1. reactants are adsorbed onto active site via weak temporary bonds
2. brought closer –> inc conc at catalyst surface
3. bonds weakened –> lowering Ea
4. orientated in righr positions for rxn –> inc freq effective collisions
5. desorbed, regenerate active site

Question 18

eqn for NO2 oxidising SO2

Answer 18

NO2 + S02 –> NO + SO3
NO + ½O2 –> NO2

Question 19

autocatalyst process

Answer 19

1. init: slow (esp if negative ions colliding: repulsion, inc Ea)
2. [Mn2+] inc, rate inc cuz it catalyses the rxn
3. rate will then dec as [reactants] dec

Question 20

rls btw substrate (loose link to reactant) and rate of enzyme-catalysed rxn

Answer 20

1. [substrate] low: active sites unsaturated, rate inc prop to [s], 1st order
2. [s] high: active sites saturated, no extra active sites to catalyse rxn, zero order

Question 21

eqn for catalytic removal of gases from car engine

Answer 21

hydrocarbon –Pt–> CO2 + H2O
CO + ½O2 –Pt–> CO2
NO2 –Pt–> ½N2 + O2
NO + CO –> CO2 + ½N2