1f Flashcards
whats kinetics all about
kinetics is all about the rate of a reaction
what do we plot to find rate
conc on y axis
time on x axis ( in seconds)
when we have a plot of conc of reactant against time,, how do we find the rate of reaction at a certain time
we find the gradient of the line at that time
rate law for 0th order reaction
rate = k[rea] ^0
anything t othe power of 0 is one so the rate = k
its a straight line slope,, still going down but not curved
rate law for a 1st order reaction
rate = k [rea]^1
rate law of a 2nd order reaction
rea = k [rea]^2
whats the differential equation for rate
- d(k) / dt
rate must be positive so we add the (-) sign
rate in terms of order
rate = k[rea]^n
where n = order
straight line equation of a 0th order reaction
[R] = -kT + [R]0
straight line equation for 1st order reaction
ln[R] = -kT + ln[R]0
y = mx + c
plot conc against time and gradient is -K
straight line equation for a 2nd order reaction
1/[R] = kT + 1/[R]0
what is rate constant k affected by
its affected by temp
equation taht shows u how k changes with temp
arrhenius
k = Ae^ -Ea/kT
lnk = lnA - Ea/kT
when u plot arrenius,, how do u find the Ea
the slope aka the gradient of the line = -Ea/R
where R = gas constant
what do u plot for the arrhenius plot
plot lnK against 1/T
what is a reaction mechanism
its the diff possible pathways a reaction can undergo
what types of reaction mechanisms are there,, theres 6 but we got told 4
- simultaneous
- opposing
- consecutive
- feedback
whats a simultaneous reaction mechanism
theres 2 possible pathways a reaction can undergo
aka 2 things happening simultaneously!!
the 2 diff routes have diff rate constants
whats an opposing reaction mechanism
u have R+S –> P with k1
but then u also have the reverse being k2
where k2 is the inverse of k1
the reaction is not in equiibrium
whats a consecutive reaction mechanism
when a reaction occurs and one occurs right after itusing the intermediate
aka 1st reaction forms an intermediate and the 2nd reaction uses the intermediate
the 2 diff reactions have diff rate constants
whats a feedback reaction mechanism
its one where R –> S –> P
but then P interferes with R
by either catalysing or inhibiting it
when we get given an overall reaction,, what cant we do
we cant predict the order of the reaction
the order must be determined experimentally
when we are given the overall equation,, what arent we given
we arent given the mechanism
the mechanism is the elementary steps that make up that overall equation
aka the RDs and the pther steps,, we arent shown the intermediate or any of that
what is the overall equatio made up of
its made up of elementary steps
and we cancel out the intermediates
and add up the same things.
what dictates the rate of reaction
the rate of reaction is dictated by the RDS
aka the slowest elementary step in the mechanism
the one with the smaller k // rate constant value
smallest k value =
RDS
if u have the equations
H2 + ICl –> HI + HCl
HI + ICl –> I2 + HCl
whats the order wrt each thing and whats the overall order
1 wrt H2,, 1 wrt ICl = total order = 2
1 wrt HI (but cant measure bc its an intermediate),, 1 wrt ICl = total order = 2
whats molecularity
the number of molecules involved in an elementary step
what value can molecularity be
1,2,3
easy on the 3 tho
the order of reaction can be what value
any value
0, fractions etc etc
whats a simultaneous equation again
where 2 things are happening at once
R–> S
R –> P
each has their own rate constant.
in a simultaneous equation,, how do we find the ratio of products after 10 mins and 1 hour
we need to find the rate ofeach reaction using its rate constant
rate = k [rea]^n
u do big k / small k = ratio of products
then u do big/small = ratio
