kinetics

Question 1

factors affecting ROR

Answer 1

concentration, temperature, catalysts

Question 2

ROR definition

Answer 2

change in []/ time taken for change

mol dm-3 s-1

Question 3

what is k

Answer 3

rate constant

Question 4

what is order of reaction to respect reactants and overall for k[H2[NO]^2

Answer 4

first order with respect to H2
second order with respect to NO
third overall (first plus second)

Question 5

state the units for k in H2 + I2 –> 2HI

Answer 5

rate = k [H2][I2]
moldm-3s-1 / moldm-3 x moldm-3 = k
k = s-1/moldm-3
k = s-1mol-1dm3

Question 6

order or reaction meaning

Answer 6

the power to which concentration of a reactant is raised in the rate equation

Question 7

reaction rate and conc

Answer 7

zero order = straight horizontal line, reaction rate doesn’t change with conc
first = diagonal, reaction rate is proportional
second = curve upwards, reaction rate is exponential

Question 8

concentration and time

Answer 8

zero = straight line
first = smaller curve downwards
second = big curve downwards

Question 9

halflife

Answer 9

the time taken for the concentration of a limiting reactant to fall to half of its initial value

Question 10

calculate k constant when H2O2 is 0.02, I- is 0.01, ROR is 3.5 x 10^-6 and rate equation is k[H2O2][I-]

Answer 10

rate = k[H2O2][I-]
3.5x10^-6/ (0.02)(0.01) = k
k = 1.72 x 10^-2 moldm-3s-1

Question 11

formula of half life

Answer 11

t1/2 = 0.693/k

Question 12

calculate the rate constant for which the half life is 17 mins

Answer 12

t1/2 = 17 x 60 = 1020 seconds
1020 = 0.693/k
k = 6.79 x 10^-4

Question 13

effect of temp on rate constant

Answer 13

when temp increases, rate of reaction increases. Rate constant is proportional the number of molecules that exceed Ea so also increases

Question 14

whar is the rate-determining step

Answer 14

slowest step in the reaction mechanism

rate of reaction depends of rate determining step so only reactants in this step is included in rate equation

Question 15

is it catalyst or intermediate

Answer 15

when something is a reactant and then becomes a product again = catalyst (used and then regenerated)

when something is a product and then becomes a reactant later = intermediate

Question 16

homogeneous catalysts

Answer 16

when the catayst is in the same phase as the reaction mixture

Question 17

hetergeneous catalysts

Answer 17

when the catalyst is in a different phase as the reaction mixture.

Question 18

homogenous reaction condiditons

Answer 18

SEP for catalyst lies between SEP of reactants

Question 19

adsorption

Answer 19

reactant molecules form bonds with atoms on the catalyst surface

Question 20

adsorption process

Answer 20

1. reactants diffuse to the catalyst surface
2. the reactant molecules are chemically adsorbed to surface and old bonds break
3. adsorbed reactant atoms react on the surface, new bonds form
4. deadsorption where the bonds between product and catalyst break
5. product diffuses away

Question 21

the iodine - peroxodisulfat reaction

Answer 21

S2O82- + 2I- –> 2SO42- + I2

redox reactions

1. 2Fe3+ + 2I- –> 2Fe2+ + I2
2. 2Fe2+ + S2O82- –> 2Fe 3+ + 2SO42-

can occur in any order.
so both Fe3+ and Fe2+ are used and then produced so they are catalysts.
two bumps on energy level profile. Catalysts used in one step and then produced in another step

Question 22

nitrogen oxides

Answer 22

SO2 + 1/2 O2 –> SO3
1. SO2 + NO2 –> SO3 + NO
2. NO + 1/2 O2 –> NO2
used in one step and then produced in another step