Balancing Chemical Equations(in detail) Video Lecture - Class 10

this is an introduction to balancing
chemical equations we're going to talk
about what it means for an equation to
be unbalanced or balanced and then we'll
learn the process that you go through to
balance a chemical equation I want to
start with a few examples that show the
concepts behind balancing equations so
you can really understand what's going
on when you work through these kind of
problems we'll begin by looking at this
chemical reaction hydrogen gas and
chlorine gas combined to make
hydrochloric acid so this is how we can
express this chemical reaction using
words and we often call this kind of
thing a word equation now we can use
this word equation to write a chemical
equation by taking each one of these
things and writing the chemical formula
for it okay so the chemical equation
looks like this hydrogen gas its
chemical formulas h2 we have an the plus
chlorine gas is CL 2 we get the arrow
and then hydrochloric acid its chemical
formula is H CL okay now if I wanted to
be really precise about things I could
put a G in parenthesis next to each one
of these to show that they're gases but
I'm trying to keep things simple for
this video now in order to start talking
about equation balancing which is the
topic of this video we have to look at
the atoms in this chemical equation we
have to look at the number and type of
atoms that we have on both sides of the
arrow I've got some diagrams here so we
can do this visually so we can actually
see the atoms at how they recombine
during this reaction okay so we got a
molecule of hydrogen gas it looks like
this we got two hydrogen atoms one two
then we got some chlorine gas we got a
molecule of that two chlorine atoms got
our arrow and finally a molecule of
hydrochloric acid so there it is one
hydrogen and one chlorine okay
so now we're going to start talking
about balancing equations and
balanced equations first thing that I
want to do is figure out whether this
equation here is a balanced equation so
here's a definition for balanced
equations a balanced equation has the
same number of each type of atom on both
sides of the arrow
okay so keeping this definition mind
what I have right here is this a
balanced equation no it's not here's why
on this side of the arrow I have two
hydrogen atoms over on this side I only
have one over here I have two chlorines
and over here I only have one so this is
not a balanced equation we don't have
the same number of each type of atom on
both sides this isn't a balanced
equation so we call it an unbalanced
equation unbalanced it's just the word
for an equation that's not balanced it
has different numbers of one or more of
the types of atoms on the two sides of
the arrow okay so this is currently an
unbalanced equation now most the time in
chemistry unbalanced equations aren't
particularly useful to us and we have to
make them balanced before we can use
them for problem solving or for doing
calculations so often chemistry we start
out with unbalanced equations and then
we have to figure out how to balance
them so in order to balance this we're
going to make a few adjustments here's
how we do it to balance the chemical
equation we change the number of these
molecules that we have and we find a
combination that gives us the same
number of each type of atom on both
sides okay it's a little bit like a
puzzle so it might turn out that to
balance this equation we need three of
these and one of these and three of
these or we might need two of these and
two of these and one of these so we play
around with the number of each one of
these that we have finding a combination
that gives us the same number of each
type of atom on both sides
okay so take a look at this equation can
you figure out what we need to do to one
or more of these in order to have the
same number of each type of atom on both
sides well here's what we do we have two
hydrogens here two chlorines here one
hydrogen one chlorine so if I get
another one of these okay if I have two
of these well then have two hydrogen's
here two hydrogen's on this side two
chlorines on this side two chlorines on
this side and now this equation is
balanced
okay so we've balanced the visual the
visual version of it to balance the
written equation what we'll do is we'll
put a two in front of the HCL here to
show that we have two of these and now
the equation is balanced okay so this is
the combination this is the combination
of these things in these things that we
need to have the same number of each
type of atom on both sides we need one
of these one of these and two of these
to end up with a balanced equation
here's another chemical reaction
hydrogen gas and oxygen gas combined to
make water the chemical equation for
this looks like this the chemical
formula for hydrogen gas is h2 that
oxygen gas is o2 and these combined to
make water which is h2o now let's look
at how we can represent this visually
okay we've got one molecule of hydrogen
gas h2 then we have one molecule of
oxygen gas o2 we got our arrow here and
h2o water is over here okay so just like
we saw previously on this side of the
equations what we start with it's our
before we've got our reactants and over
here is our after our products okay so
take a look at this equation and these
atoms here and think about this is this
equation balanced the way it's written
here an answer is no it is unbalanced
here's why I've got two hydrogen's here
and two hydrogens here's the hydrogens
do balanced
but the oxygens don't I have two oxygens
here and only one over here so this
equation is not balanced as it's written
in order to change this we're going to
adjust one or more of the numbers of
these different compounds okay
here's how we're going to do it take a
look I've got two oxygens here and one
here so the first thing I want to do is
I want to try to balance these oxygens
to get more oxygens on this side to get
two oxygens on this side I'm going to
add another one of these h2o and I have
two of them alright so I have two
oxygens here two oxygens here the oxygen
is balanced but check this up by adding
this water here I change something else
my hydrogens used to balance but now I
have four on this side I don't have two
on this side but that's okay because I
can change the number of these as well
okay I used to have one so let me add
another hydrogen here now I have four
one two three four hydrogen atoms over
here one two three four hydrogen atoms
over here okay so now this is a
representation of how the atoms balance
in order to balance the chemical
equation up here I'm going to put a two
in front of the h2 because I have two of
those and then I'm going to put a two in
front of the h2o here because I have two
h2s and now the equation is balanced
here's a really common mistake I've got
to tell you about when people are first
learning this stuff a lot of the times
they'll say hey I have a simpler way to
balance this here's how you do it get
rid of this 2 here get rid of this 2
here and then just put a little number 2
right under this
oh here now you have h2 on this side h2
on this side Oh 2 on this side and o2 on
the side it balances perfectly yeah but
unfortunately it can do that these
numbers here we call them subscripts you
can't change them when you're balancing
an equation they have to stay the same
and here's why
in this equation we're talking about
water its formula is h2o and this is
what a water molecule looks like if you
put it to here we're not talking about
water anymore we're not talking about
h2o anymore we're talking about a
molecule like this with two oxygens and
two hydrogen's this isn't water this is
now a compound called hydrogen peroxide
so yeah by adding this to you might
balance the equation but it's no longer
the equation for hydrogen gas and oxygen
gas making water it's now the equation
for hydrogen gas and oxygen that's
making hydrogen peroxide you totally
change the meaning of the equation if
you mess around with these subscripts so
you can't do that the subscripts have to
remain the same but you can put numbers
in front of one or more of the compounds
but the numbers always have to be in
front you can't modify any of these
subscripts when we first start off
talking about balancing equations I love
to use visuals like these of the atoms
and molecules so you can really see
what's going on but when you're gonna be
balancing equations on homework or on
quizzes you're not gonna be using
drawings like this instead you want to
be able to balance equations using
charts doing a little bit of math so I'm
going to show you one example here of
how you do that okay so in this equation
we have nitrogen and hydrogen now
obviously we have those on both sides so
I've made this little chart nitrogen and
hydrogen on both sides so the first
thing you want to do is you want to
write in your chart how many of these
atoms you have right so we have n2 so
that means that we have two nitrogens on
this side you can see that from the
diagram h2 we have two hydrogen atoms on
this side and then we have the arrow and
then over here we have n so we have one
nitrogen atom and then we have three
hydrogen atoms so to start balancing
this you want to look at where you have
an imbalance of atoms where you don't
have the same number of atoms and you
want to think about what you could
multiply one of these compounds by okay
so let's let's look at nitrogen right
here
we have two nitrogens here we only have
one here okay so one thing that we could
do to start out balancing this is we
could put a two in front of nh3 here so
that would multiply this whole thing by
two so now we'd have two of these and
that would give us two nitrogens and now
we have two times three which is going
to give us six hydrogen's okay so that's
how we use this chart now that kind of
changed these numbers so let's look at
what's going on over here okay
so now the nitrogen is balanced but now
the hydrogen's don't bounce I have six
here and I have two here okay
so what could I multiply something by
here to fix the hydrogen's well I have
two right now I want six so I could put
a 3 in front of this it would look like
this in our visual now we have two more
hydrogens and that gives us 3 times 2 6
hydrogen's here so we can keep track of
these adjustments that we make using
charts like this that show us how many
of each atom we have on both sides we
multiply something by a number in front
of it and then we change the number of
atoms so the best way to get good at
this is to just do a whole bunch of
practice check out my video of balancing
chemical equations practice problems
you'll do a whole bunch of examples and
it will really make sense