Reaction Equilibria for Simultaneous Reactions Video Lecture - Civil Engineering (CE)

okay this is a consecutive reaction what
it says you have our simultaneously the
same thing they want you to write the
overall reaction and list the
intermediates this is a highly difficult
question what you're essentially going
to have to do is add these up and make
sure the intermediate is canceled it
gives you a hint
it says the answer involves the
manganese or oxide you know that's in
the answer in the reactant and you know
in the product you have the manganese
three oxide
okay there might be other stuff most
likely it's going to be co2 and the
product and some CEO and the reactant as
well but those are the main Guinea is
that it tells you in the question that
you're going to happen okay so we
essentially have to manipulate these
equations until they add up and get rid
of everything else understand the
question yeah okay so yes kind of
involved here's how I do these problems
you look this is what I want
let's find it up here I think this is
the only place it appears you also want
this mn 2 O 3 and that appears here ok
let's see what doesn't appear here as
far as the manganese goes well this one
here I'll put it in a box
M and 304 it appears in two places
that doesn't appear in a final reaction
also this one doesn't appear I'll Circle
it MN o the manganese to oxide what do
we call these ones that are in a fox or
a circle not spectator ions
intermediates so that goes for the thing
in the box and I think one circle okay
so you know that you know the answer for
Part B I think without starting the
question so what you want to do is add
this up so that you get what they asked
for which is the manganese four in the
main these three and that you cancel out
the ones that are not asked for the co2
is we don't care we don't care about the
carbon dioxide or monoxide or you're
just going to let it fall out as it does
all right so what I'm going to do I'm
going to start with this here do you see
how a manganese 4 oxide here and that's
here that's good it's in the reactants
here so when I add this up this is just
gonna carry on down right there that's
totally fine let's look at this I need
this in the products unfortunately over
here it's in the reactants you see that
so what I'm going to do take this whole
reaction first of all I want to flip it
make it backwards so that this is in the
products because I wanted it in the
products that okay
so I'm gonna multiply by a negative also
I want one of them and I have three
okay so I don't want flyby one then
negative to flip it the one third to
give us one of them cool so far okay
it'll get worse so don't worry the next
part I want to do and once I multiply by
some one equation I'm done with that
equation I'm not going to multiply it
yet again it's fixed so now I want to
mess with these talk to since this is
fixed I'm going to make sure that this
thing in the box gets us out I wanted to
cancel out with this is that okay so
this one here now here's the weird part
right now after the multiplication is
this in the products or reactants where
is this it's in the reactants because I
flipped it with this - okay well I don't
want this to be in the reactants because
it's got a cancel so I've got to flip
this one too -
and how many of these will have 2/3 that
and so I need two thirds of these so
they cancel okay
but the second reaction let's go up to
the top what else do I want to cancel
you have to ask yourself well this time
I know fast cancel okay where is this
reactants or products it's in the
reactants cuz I flipped it so this is
good I'm gonna leave this here I don't
need to flip this because if this is the
reactants it'll cancel what's in the
products so I'm not gonna multiply by
negative here but I have how many of
these two three times 2/3 is two so I
need two of these
okay I'm done with the multiplication
now if I can add I'm done so I'm gonna
have two of these I'm gonna have one of
these all the other manganese are gonna
cancel I just want to look to see what
happens with the co2 what is 2 minus 2/3
minus 1/3 what is that 2 minus 2/3 minus
1/3
one good see that would easy
and how about over here 2 minus 2/3
minus 31 done questions this disgusting
animal it will not get harder than this
this is this positive yes like this
spectators
they're met they don't have a particular
name all right yeah it's those molecule
we were like the third equation is you
that's the second and flip it so the co2
cancel if these are there so it's kind
of match it up with the co2 so as
canceling as long as you have a pink
product you could try that I don't know
if it would work you need to make sure
that all the other manganese species
cancel out yeah
so if that happens that's fine I do it I
for me this is the most systematic way
to do it there's different ways you can
kind of logic it do the logic in your
mind but I just want to kind of my logic
is first I make sure that what I want is
here and so that's why I did this first
multiplication with this one and with
this one and then after that I make sure
that my intermediates are going to
cancel once I've got those two I know
I'm done so then I just have to like do
the addition and stuff that's why logic
but if you want to do you could try that
if you add it up and you get other
manganese that shouldn't be there
you just got to start over