00:01
We are asked to solve for the enthalpy of the following equations.
00:06
We have three using average bond enthopies, which are found in a table in your text.
00:15
I like to do these by finding all the entopies or finding all the bonds and then crossing out those that are duplicated on each side of the equation.
00:28
And to calculate bond entopies, we take the energy, the delta h.
00:37
I'm going to write this up here in a different color.
00:43
We take delta h of bonds broken minus delta h for the bonds formed.
01:07
So we take reactants minus products.
01:12
But we don't have to worry about the bonds that remain the same.
01:18
So let's look at our first substance.
01:21
And i'll do our first substance in a blue.
01:25
And our first substance right here, we have four c -h bonds.
01:32
And we have one c double bond c bond.
01:44
In our second substance, we have 1 o double bond, or o bond, o dash bond, single bond.
01:56
And we have two oh bonds.
02:05
In our next substance, i'm going to get my highlighter going here.
02:11
I'm going to highlight our ch bonds.
02:15
One, two, three, four.
02:20
So we have four, whoops, we have four.
02:27
C -h bonds.
02:32
I have, i don't know if i can highlight in this color very well, one, two, o -h bonds.
02:56
I have one, two -c -o bonds.
03:15
And the bond i don't have highlighted yet is my one -c -c -c bond.
03:34
Very good.
03:35
Now let's take a look at the bonds that on each side are the same.
03:45
I have four ch bonds in this side and four ch bonds on that side.
03:51
That means i'm not going to cross them out yet.
03:56
I have 2 -0 -h bonds and 2 -0 -h bonds.
03:59
If you look at the bonds i have listed right now, those are the bonds that we're not going to cross out.
04:08
So these and these were not broken.
04:11
These and these are not broken.
04:13
There's some people who just look at these and decide which bonds to include.
04:18
I'm not one of those.
04:19
I prefer doing them like this.
04:22
So now i look up in the table and i find out that this bond is 614 kilojoules per mole.
04:38
And there's one of them so i don't have to do anything.
04:42
Next i have my o bond.
04:45
There's one of those.
04:46
And when i look that up in the table, it's 146 kilojoules per mole.
05:00
I'm just going to bracket these because those are my bonds broken.
05:03
Now i'm going to subtract from that my bonds formed.
05:07
I have one c -o bond formed.
05:11
Or i have two of those...