00:01
We are given these four reactions with their corresponding delta h values, and we're asked to determine the delta h value for the reaction of calcium solid with two moles of c graphite to produce one mole of calcium carbide cac2 solid.
00:33
Actually, we already know that one.
00:35
That was the first one that they gave us.
00:38
Ca solid reacts with 2c graphite to produce cac2 solid.
00:56
Delta h for that is negative 62 .8 kilojoules per mole, and we want to figure out the delta h for the reaction of cac2 solid plus two moles of h2o liquid going to caoh2 aqueous and c2h2.
01:36
So we need cac2 on the left -hand side, just one of them.
01:45
So we're going to have to reverse the first reaction.
01:48
If we reverse the first reaction, we change the sign from negative to positive.
01:56
We also want c2h2 on the right -hand side, so we're going to have to reverse this reaction.
02:07
Again, if we reverse the reaction, we change the sign from negative to positive.
02:11
Then we want one caoh2 aqueous on the right -hand side.
02:22
That's what we have here, and we want two liquid waters on the left -hand side.
02:30
The only reaction, i think there's a couple, this one has water and this one has water.
02:38
This one's already reversed, giving us two waters, so i think we're probably good.
02:44
If we add these up, then we see that the calciums are going to cancel because this reaction has been reversed.
02:59
Our calcium oxides are going to cancel...