00:01
For the first part of this question, we're trying to find the change in enthalpy for the combustion of acetylaldehyde.
00:06
And then for the first step, we're using the enthalpy of formation method.
00:11
So the equation that we're trying to find the change in enthalpy for is the acetylaldehyde, ch3cho, and it's the combustion.
00:25
So we're going to add acetylaldehyde to oxygen, and then it's going to form carbon dioxide and water.
00:37
Now we need to balance the equation, which i'll just do quickly here.
00:41
And this should be two and a half.
00:45
So this is the balanced chemical equation that we're trying to achieve.
00:48
So we're going to basically add those three formation reactions they give us in order to calculate the change in enthalpy.
00:59
So we're going to use the other reactions as kind of a addition problem.
01:03
So we want to arrange the equations so that way it looks like the given.
01:08
So the first formation reaction has the acetylaldehyde in the products.
01:13
We want to turn it into the reactants.
01:15
So we're going to flip that reaction.
01:19
So that way we have acetylaldehyde as products.
01:23
Products and then that's going to go to two carbons plus two hydrogens plus half an oxygen and then its change in enthalpy is negative 170 .7 because we reversed the reaction the sign is going to go from negative to positive so it's going to be a positive so we'll have carbon plus oxygen going to co2 with its change in enthalpy, which will be the same.
02:21
And then we have h2o2 plus co2 plus co2 plus co2.
02:24
Plus o2 goes to water.
02:29
And then we can write its enthalpy over here.
02:36
Before we start crossing things out, notice that we have two carbon dioxide and two waters up here.
02:43
So we're going to have to take these two equations times two.
02:50
So we're going to take everything in the equation times two, including the enthalpy.
02:53
So we're going to have two carbons, two oxygens, two carbon dioxide, oxides, and then we're going to take this times two.
03:01
Same thing for the water.
03:02
We have two here.
03:04
Two times a half is going to be one, two, and then we take this times two.
03:10
Now let's see if we can start crossing things out.
03:13
So these two carbons on the left cross out with two carbons on the right.
03:18
Same with the hydrogens.
03:21
The two hydrogens here cancel out the two hydrogens on the left.
03:24
Remember remember, they can only cancel out if they're on opposite sides.
03:28
And then let's look at the oxygens.
03:34
We have two oxygens here, one oxygens here.
03:37
So we have a total of three on the left.
03:39
And then we have a half over here.
03:43
So we can cross it out from either.
03:48
Oxygen doesn't matter.
03:49
So we'll cross out a half here.
03:51
We'll cross out the one here.
03:52
And then this is going to turn into half again.
03:54
In.
03:56
So now if we look, we should have the exact same equation that we have on top, which we do.
04:01
So let's just kind of add everything together.
04:03
So we have our ch3, our acetyl aldehyde plus two and a half oxygens going to two carbon dioxide plus two waters...