Average & Instantaneous Rate of Reaction (Part - 2)- Chemical Kinetics, Chemistry, Class 12 Video Lecture

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correctly so let's see a reaction from
macroscopic level I mean I have a
reaction I am going to concern only what
the rate rate is the only thing that is
in my mind now right so if I at the
macroscopic level I'm not going in the
molecular level and a very Burdine you
level you can see what I do only from a
distance I am seeing it there is a
container and something is happening I
can just seen the quantity of reactants
quantity of product those things I am
seeing then I call it a macroscopic
level I'm not even concerned about which
molecules are reacting why they are
reacting I am concerned only the
macroscopic level
I have only interest me the amounts of
the reactant reacted and the amount of
product form right amount of this amount
on this just what I am interested and
that is what we call macroscopic level
but you're going to talk about the
microscope molecular level where you
actually want to see the molecules how
it is taking part how they are reacting
right so if you see for a given reaction
if you go inside any of reactant has
will have atoms and molecules all right
so you want to see what is happening
what is actually happening inside why a
plus B is becoming CLE so you see the
molecules of a are in blue being red
seeing green and D in red you see they
are reacting right there they are
bumping each other and they are forming
new products this is something at very
very microscopic level or molecular
level record because here in this level
we are concerned about the reaction
mechanism how it is reacting right there
orientation the energy of these
molecules and how they are getting
undergoing collisions and what is the
effective collision which is non
effective collision how the product is
getting formed all those kind of things
role of catalyst also how how the
catalyst is helping to increase the
reaction rate so this is all molecular
levels in in chemical
kinetics will discuss the reactions both
at macroscopic level and molecule level
correct so in this whole Safran we'll
first start with macroscopic level we
will talk about the change in the
product or change in the reactant
concentration and once we understand the
concepts why the products are how the
rate of change of product is linked with
other parameters then we'll start at
molecular level about how the molecules
interact and the product is getting
formed okay so molecules at the
molecular level I will assume the
modules as car and the bumping of
molecule which you see here is similar
to bumping of cars correct so you see
these are my cars and if the car bumped
each other at a very high speed and they
almost ramp each other right the brick
one of that then I call a reaction
happen right for example in this case
you see the two car in the first case in
the first case if you see these two cars
RAM and the reaction happened but in the
second case if you see the cars didn't
even touch each other there was no
reaction here there was no reaction here
and there is a reaction here so in the
whole chapter will consider molecules as
car and we'll try to understand how the
reaction is happening maybe we talk
about the feasibility of the reaction in
this case here the action was feasible
here it didn't happen
we talked about the extent of the
reaction then we'll talk about the
number of cars we have right in the blue
cars in the red cars and that will
depend they will define the extent of
the reaction we talk about the speed of
the reaction then also we'll talk about
a lot of factors this deity will try to
visualize molecules as car in the whole
chapter and the way the molecules bump
each other there is nothing about the
bumping of two different cars and the
final broken car is my product
he'll assume in that pain we'll see the
whole chapter right the mounting of God
this becomes a new product so since I
told that we'll talk about molecules as
car in the whole chapter let's see in a
car what is their car grunts right this
is a speed of the car example is a card
and this is my distance time graph I
have made and there's a car which will
move from here to here and if you see if
the time goes Carvin moved from point A
to point B so this is my point
a and this is my point B actually so if
you see the car is moving from point A
to point B and it's going up and now
it's stopped but the time is kinetically
stop and then again going up the higher
speed and pause for some time and then
again it goes up and it stops this is
the distance thing obviously the
distance covered let me repeat once
again the car starts the car accelerates
and then it stops it stops for certain
time time goes on and then car gain
starts again goes off store for some
time again the car starts and then it
stops so if this is if you plot this
diagram this is hot look right now if
you see in this whole journey to talk
about the average speed of the car that
is nothing but total distance covered by
car that is a B by total time this is my
point here B if you plot the XY point
here this is X maybe T and Y will be
point Li correct here beti will be zero
and point a so if you see the total
distance covered as a B and total time
is T so if you talk about the average
speed average will be total distance
covered by total time there is nothing
but a B by D oh it took 2 T seconds to
come from there to there that will be
the average speed correct from point A
to B but now if you want to find the
instantaneous
and you must have started this in the
this chapter the instantaneous speed at
any point instantaneous speed at any
point nothing but if from that point you
draw tangent and the slope of this
tangent will give you instantaneous
speed that is DX by D right that is
speed is changing here this is a very
simple concept we have learn in physics
average speed and instantaneous P if you
have not solid and if you're not
understanding from the slide you can
watch the physics video where we explain
the instantaneous speed and average
speed so here we have this an
instantaneous speed for air at any given
point for example here also I can find
the instantaneous speed I just have to
draw a tangent here and the slope of
this will give me an agent in a speed at
this point if you see the timing will be
in this direction and the speed will be
zero at this point there isn't any speed
will be different right if you see here
it is accelerating it has more speed
here it is almost zero speed so at any
given point in time you can just draw
tangent will get a instantaneous speed
at this point of time similarly in the
reaction also we will find the average
rate of the reaction and instantaneous
rate of reaction they told the molecules
are nothing but car a just comparing car
has average speed in sydney a speed so
the reaction will also have average
straight and is it in this you see this
is a technical reaction we have so if we
see a typical reaction have reacted in
my left hand side product on the right
hand side over a period of time the
reactant will diminish and will get both
products if you see this graph the
concentration of reactant goes down as a
time increase the concentration of
product in the red one increase at the
time increase the green one is by
reactant and the radio is my product
that's my typical concentration time
graph for a given reaction so if you see
for the end of reaction you can define
the rate of reaction rate of a reaction
will be nothing word change in
change in amount of chemical species it
can be species can be anything reactant
or product right during a reaction
reaction the whole thing divided by time
in which change was caused for example
you mix hydrogen an oxygen you get water
the reaction took only two seconds but
you're observing it for maybe thirty
minutes but the reaction time will be
two minutes because of the two for a two
second because in two seconds only
actually the reaction happened right
example you have hydrogen and oxygen it
gives water and this took only two
second correct and after that it was
just water and you just observing it so
it is not the time you are observing it
is the time when the reaction is
happening actually so that is the time
it will divide and this is the change in
the amount of chemical species during a
reaction for example we talked about the
decrease in the concentration of
hydrogen or decrease in the
concentration oxygen or the or increase
in the concentration of water so as we
have told a chemical rate of reaction
will have average rate of reaction and
we have again in sent a nice rate of
reaction similar to car average speed
instantaneous speed so let us talk about
the average rate of reaction right so
average rate of reaction is nothing but
the rate of decrease in concentration of
any of the reactant because the
concentration of reactant will decrease
or the rate of increase of concentration
of product okay either rate of decrease
in concentration of any one reactant
little bose you have a plus B is equal
to C plus D or simply
a plus B here and you have C plus B here
so talk about the average strength there
is nothing but the rate of decrease in
concentration of anyone on the reactant
for example a or b correct so if you see
we want to write average rate this is
nothing but minus Delta n because the
number of moles I'm talking about of
reactant by delta T or you can say Delta
n of product by please note there's a
negative sign here and there is no sign
here it is a positive sign here why this
is negative sign because if Z the
reactant will decrease for example at T
is equal to zero it was let's suppose 10
volt and it was 2 volt at T is equal to
T this will be bounded suppose five volt
and it suppose this is the increase it
becomes six one so if we see the change
in the reactant is what 5 - 10 3 is
minus five so since this is a minus here
to remove that - we have to take an exit
sign but you talk about the change in
product final minus initial six - to do
this for already a positive quantity
maybe once again the change in reactant
final minus initial it is 5 - 10 it is
minus 5 so to get rid of minus sign in
put a minus sign here changing products
final minus initial plus 6 minus 2 is 4
as a positive number so we won't put up
negative sign here correct so both are
nothing but average it you can just
either take the rate of decrease of the
reactant or rate of increase of the
product both are nothing but in the rate
of reaction let's talk about the
instantaneous to the variolation
see again instantly in this tube
reaction as a tone it is nothing but at
any given point of time for example if I
want to know here here I can find - dr
by dt so da by it will be this much you
put a - you get this much this slow
this is my instantaneous rate of
reaction or if you point for the product
it will be + DP by dt y + and - the same
rule vitiated just explained saying this
is this is my dr way into this line but
the moment you put - the sign changes
you become something in this direction
if you see both are in the same
direction at any given point of time so
rate instantaneous is nothing but either
- dr by dt or + DB by both are mine
instantaneous rate of the reaction
one thing to note here is when i talk
about the average you know reaction it
doesn't mean that you have to talk about
the average rate from here to here i can
also talk about the average rate from
here to here this point is from level
this point is a this point of B I can
also talk about the average in between a
and B so in that case I'll find the
concentration at B and find the
concentration of a for example in this
case average rate from A to B we watt
concentration that this B are at B minus
concentration at a by delta T how much
time it took from here to here that is
it took this much time
correct and since you see our B will be
less than re there has to be a negative
sign because it's nothing but for the
reactants or the I can it was minus of
Delta we have identity so this is my
average trade with these two points a
and B correct so we talk about the
average you have to talk about the
average rate of reaction between two
points when you talk about instantaneous
you talk about insert a nice rate of
reaction at a given point of time right
two point average one point
instantaneous thank you visit exam
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