00:02
According to hess's law, we have a forming b added with reaction c forming d.
00:13
If we add these two reactions to get a plus c forming b plus d, the delta h of this reaction is obtained as the sum of the delta h of the two reactions we added to form it.
00:28
So in this problem, we're given with three reactions and out of these we want to derive the desired reaction.
00:36
So first let's write those given reactions n2 plus o2 to form 2no.
00:45
It's called this as reaction 1 with delta h1 given as negative 180 .5 kj.
00:54
The second reaction is n2 plus 3h2 to form 2nh3 with delta h of negative 91 .8 kj.
01:12
The third reaction is h2 plus o2 to form h2o delta h equals negative 483 .6.
01:28
So from here we're going to derive the desired equation which is 4nh3 plus 5o2 to form 4no plus 6h2o.
01:54
So what we will do is that we need nh3 in the left side but in the second equation we have that on the right side.
02:02
So we will reverse equation 2 and aside from that multiply it by 2 to double nh3.
02:09
So doing that gives us 4nh3 giving 2n2 plus 6h2.
02:20
As a result, the enthalpy change will give as a result of reversing it that sign will also change from negative to positive and the result of multiplying by 2 is that it will be also multiplied by 2...