Kinetics I & II Flashcards
5 Br- + BrO3+ 6 H+ -> 3 Br2 + 3 H2O
Rate = k [Br-] [BrO3-] [H+]2
Explain why Br- is not a fifth order reactant, despite 5 Br- appearing in the stoichiometric equation.
it in unlikely that 5 Br- ions will collide simultaneously
What is rate of reaction
the change in concentration of a reactant or product per unit time
What is the order of a reactant
the power to which the concentration of the species is raised in the rate equation
What is the overall order of reaction
the sum of all individual orders
What is the half life of a reactant
the time taken for the concentration of the reactant to fall to one half of its initial value
What is the activation energy of a reaction
the minimum energy needed for successful collisions, leading to a reaction
What things need to be met in order for a successful collision
- a collision between particles
- in the right orientation
- with enough activation energy
describe what a 0 order concentration time graph looks like
Concentration is straight down over time, often intercepts the x axis
describe what a 1st order concentration time graph looks like
curve downwards
describe what a 2nd order concentration time graph looks like
a curve downwards with a slight bend, can be distinguished using half lives
describe what a 0 order rate concentration graph looks like
a straight line across, parallel to the x axis
describe what a 1st order rate concentration graph looks like
a directly proportional line straight diagonal
describe what a 2nd order rate concentration graph looks like
A curve line upwards
what are the units of rate
mol dm-3 s-1
What would the units for k in rate = k be
mol dm-3 s-1
what would the units for k in Rate = k[A][B] be
mol-1 dm3 s-1
what would the units for k in Rate = k[A]2[B] be
mol-2 dm6 s-1
what is shown in the rate equation
the species that are in and leading up to the rate determining step
what is the molecularity of a reaction
The “molecularity” of a reaction step describes how
many particles are involved in that step.
what does it mean to quench a reaction
introducing a material that combines with any unused reactants and effectively stops a reaction from continuing
draw an arrhenius graph
use y = mx + c
where y = ln k
mx = Ea/RT
c = ln A (y intercept)
so graph should look like….
y (axis) = ln k
x (axis) = 1/T
gradient = -Ea/R
y intercept = ln A
what colour is I- ions in solution
colourless
what colour is I2 in solution
dark orange/brown
when we add starch to our titrated solution of thiosulfate ions and iodine, what tells us we have reached close to the end point, and what is an indicator that we haven’t added enough thiosulfate
reached close to the end point will show us a pale yellow, almost colourless solution even with the starch added as there is no more I2 left in the conical flask
an indicator that we haven’t added enough thiosulfate is that the solution turns black when adding starch, as the starch reacts with I2 to produce a blue black colour
why do we add starch indicator later on when titrating thiosulfate with iodine
in iodine, a mixture of I2 and I- exist, and there react to make I3-
I3- forms complexes with starch and gets trapped inside its helical structure
Therefore we do not see that sharp colour change as iodine is being used up before the indication point
what is on the x and y axis on a rate-concentration graph
rate is on the y axis, concentration is on the x axis
what is on the x and y axis on a time-concentration graph
time is on the x axis, concentration is on the y axis
are catalysts included in the rate equation
YES, but only is they are included leading to or in the rate determining step
