00:01
So if you want to measure a change in enthalpy, it's helpful to think about, well, what is enthalpy when you get right down to it? and we sort of have a definition of enthalpy being the energy plus the pressure volume product.
00:17
And so what we can do here is, well, if we want to talk about the change in enthalpy, that will be equal to the change in energy plus the pressure times change.
00:32
Change in volume plus the other product, which is the volume times the change in pressure.
00:39
Okay.
00:40
And remember delta e here, we can think of as the heat plus the work, which we define work as negative p delta v.
00:51
And i'm just going to add in the subsequent terms here.
00:55
Sorry, let me try that again.
00:57
Pressure delta v.
01:00
Let me try that one more time.
01:02
Pressure delta v plus the delta p lovely and what you'll see here is that the pressure change in volume actually cancels out here and so what we end up with is that the change in enthalpy is really equal to the heat plus the product of the volume and the change of pressure and oftentimes when we're talking about enthalpy we're talking about chemical reactions that you you would do on a bench top.
01:34
And remember, if you think about, you know, let's say you have a beaker of solution and you have your reaction happening inside your solution, things are reacting, but the pressure involved here, remember, so it's the pressure of the atmosphere.
01:52
So this is the external pressure applied to the system.
01:56
That's this pressure here...