00:01
Consider the following reactions, right? so these are the equations given to us on the screen i have written.
00:07
Now it is as that you have to calculate the enthalpy change for the reaction c2h6o plus 302.
00:17
That gives 2 co2 plus 3h2.
00:20
Right? so this is so simple, right? you just have to do one thing, right? let us just suppose this equation number one.
00:29
Let me just suppose it equation number one this is equation number one right and this is equation number two right so out of these we have to just give the operations right so that we can get the equation this right this is what we want right so out of the out of that we will just apply the operations in del age as well right this is what we have to do now we want here c2h6 o right so where is c2 h6 o here you can see c2 h6 o on the right hand side right so what you could do is we want this in on the left hand side as well as we want it to be divided by two right so that we can go we can get the value equation uh in the number of moles as a number of moles equals to one for this this is desired value right so now what you could do is you could write negative of you have to just subtract somewhere so here you can write let me just write here half okay so it must be it must be negative of half can you write this yes now for this equation we have 302 now we want 3 .02 now we want right we want 3 o2 so from this you want 3 o2 that means we have already minus of half of o2 is already there from equation number 1 but we want but we want 5 operating this we want something uh this is 5 o2 we have 5 by 2 o2 right and we want only 3 .02.
02:46
Right.
02:46
So how is that possible? okay.
02:55
So let me just leave now, leave it for now.
02:58
That is for o2.
02:59
I'm just taking 2h2 in account, right? so here when you applied minus half, that is minus half of h2o, that will be h2o, right? and here when you simply add it, you will be getting h2 only, right? but we want, but we want it to be, we want on the right hand side, right? we want it for the right hand side, right? right.
03:40
So now you have to apply the operation here, right? so that means you can say that you can write here, you want to get 3h2, right? but we are talking about right inside, right? so this must be what? this must be minus 3h2o, right? we are taking on the left hand side right now.
04:05
When you put this on the left hand side for the final equation, right? so you will be getting minus 3h2o, right? so we want minus 3h2 for now, right? let us just understand in this way.
04:18
So now 2h2 is there already there, right? so we want to make it minus 3h2.
04:25
Right.
04:26
So what you could do is minus of 3h2.
04:29
That means minus 3 by 2...