00:01
For this question, we're given these three reactions with their corresponding delta h values, and we're asked to find the delta h of formation of gaseous hcl.
00:11
The reaction for the formation of hcl is going to be one -half h2 plus one -half cl2 going to one mole of hcl, and we want to find delta h for this reaction from these reactions.
00:35
So we'll employ hess's law.
00:38
We need to get hcl on the right -hand side, so we're going to have to reverse this last reaction.
00:47
When we reverse the reaction, we change the sign on delta h.
00:52
Now we have one mole hcl on the right -hand side.
00:56
Then we're going to need, i forgot a two right here, so we need one -half h2 on the left -hand side, and we can get that if we reverse this reaction.
01:23
We change its sign, and we multiply it by one -half, and then we multiply this by one -half.
01:39
Then we need to multiply this reaction by one -half, so we'll multiply delta h by one -half.
01:55
Then we see that because this reaction was reversed, the nitrogens cancel...
