00:01
All right, so for this question, we're given the three reactions in black and given their respective changes in enthalpyes for those reactions.
00:08
We're asked to use these reactions to find the change in enthalpy of the reaction in blue.
00:14
So to do that, we're of course going to have to use hess's law.
00:16
And to do that, we're going to have to manipulate the reactions in black in order to get, once we add them together, get the reaction in blue.
00:24
So first thing i notice is that hydrogen gas, just mono -hydrogen gas, that needs to be a reactant, but in this case it's a product.
00:34
So we're going to need to flip it.
00:35
We're also going to need divided by two, because we don't need two moles of it.
00:38
We only need one.
00:44
One half.
00:47
And so if we flip it and we divide it by two, we're going to need to multiply this enthalpy by negative one half, which is going to give us its actual change in enthalpyy of negative 218 .2 kilojoules per mole.
01:22
All right, it's the same for monobroming gas.
01:29
We need it as a reactant, but in this reaction, it's a product, and it's twice as much as we need...